Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $183.77   11.243%   $204.4313   $204.43   $204.45   $204.40  
  Purchase #2 $158.38   8.631%   $172.0498   $172.05   $172.05   $172.00  
  Purchase #3 $247.67   10.211%   $272.9596   $272.96   $272.95   $273.00  
  Purchase #4 $141.49   13.868%   $161.1118   $161.11   $161.10   $161.10  
  Purchase #5 $166.54   11.450%   $185.6088   $185.61   $185.60   $185.60  
  Purchase #6 $199.30   12.184%   $223.5827   $223.58   $223.60   $223.60  
  Purchase #7 $230.90   6.388%   $245.6499   $245.65   $245.65   $245.60  
  7 purchase totals = $1,328.05       $1,465.3939   $1,465.39   $1,465.40   $1,465.30