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 $183.99   11.695%   $205.5076   $205.51   $205.50   $205.50  
  Purchase #2 $230.53   3.462%   $238.5109   $238.51   $238.50   $238.50  
  Purchase #3 $41.77   5.444%   $44.044   $44.04   $44.05   $44.00  
  Purchase #4 $164.97   7.181%   $176.8165   $176.82   $176.80   $176.80  
  Purchase #5 $151.81   3.264%   $156.7651   $156.77   $156.75   $156.80  
  Purchase #6 $5.46   13.827%   $6.215   $6.22   $6.20   $6.20  
  Purchase #7 $247.28   8.496%   $268.2889   $268.29   $268.30   $268.30  
  7 purchase totals = $1,025.81       $1,096.1480   $1,096.16   $1,096.10   $1,096.10