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 $57.56   5.443%   $60.693   $60.69   $60.70   $60.70  
  Purchase #2 $229.29   11.529%   $255.7248   $255.72   $255.70   $255.70  
  Purchase #3 $217.81   13.408%   $247.014   $247.01   $247.00   $247.00  
  Purchase #4 $205.34   5.363%   $216.3524   $216.35   $216.35   $216.40  
  Purchase #5 $249.95   10.413%   $275.9773   $275.98   $276.00   $276.00  
  Purchase #6 $240.62   8.163%   $260.2618   $260.26   $260.25   $260.30  
  Purchase #7 $94.78   9.842%   $104.1082   $104.11   $104.10   $104.10  
  7 purchase totals = $1,295.35       $1,420.1315   $1,420.12   $1,420.10   $1,420.20