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 $244.66   7.688%   $263.4695   $263.47   $263.45   $263.50  
  Purchase #2 $59.56   4.645%   $62.3266   $62.33   $62.35   $62.30  
  Purchase #3 $22.36   12.367%   $25.1253   $25.13   $25.15   $25.10  
  Purchase #4 $18.26   12.422%   $20.5283   $20.53   $20.55   $20.50  
  Purchase #5 $46.81   3.666%   $48.5261   $48.53   $48.55   $48.50  
  Purchase #6 $137.31   9.709%   $150.6414   $150.64   $150.65   $150.60  
  Purchase #7 $232.89   3.607%   $241.2903   $241.29   $241.30   $241.30  
  7 purchase totals = $761.85       $811.9075   $811.92   $812.00   $811.80