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 $96.56   13.140%   $109.248   $109.25   $109.25   $109.20  
  Purchase #2 $88.63   6.196%   $94.1215   $94.12   $94.10   $94.10  
  Purchase #3 $120.25   11.284%   $133.819   $133.82   $133.80   $133.80  
  Purchase #4 $169.50   4.251%   $176.7054   $176.71   $176.70   $176.70  
  Purchase #5 $216.97   4.664%   $227.0895   $227.09   $227.10   $227.10  
  Purchase #6 $97.76   5.312%   $102.953   $102.95   $102.95   $103.00  
  Purchase #7 $149.40   6.703%   $159.4143   $159.41   $159.40   $159.40  
  7 purchase totals = $939.07       $1,003.3507   $1,003.35   $1,003.30   $1,003.30