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 $59.59   9.493%   $65.2469   $65.25   $65.25   $65.20  
  Purchase #2 $112.98   4.552%   $118.1228   $118.12   $118.10   $118.10  
  Purchase #3 $169.42   8.586%   $183.9664   $183.97   $183.95   $184.00  
  Purchase #4 $145.31   11.131%   $161.4845   $161.48   $161.50   $161.50  
  Purchase #5 $223.73   10.328%   $246.8368   $246.84   $246.85   $246.80  
  Purchase #6 $74.77   3.391%   $77.3055   $77.31   $77.30   $77.30  
  Purchase #7 $168.50   10.712%   $186.5497   $186.55   $186.55   $186.50  
  7 purchase totals = $954.30       $1,039.5126   $1,039.52   $1,039.50   $1,039.40