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 $51.69   6.290%   $54.9413   $54.94   $54.95   $54.90  
  Purchase #2 $41.75   10.442%   $46.1095   $46.11   $46.10   $46.10  
  Purchase #3 $60.98   11.482%   $67.9817   $67.98   $68.00   $68.00  
  Purchase #4 $217.92   10.712%   $241.2636   $241.26   $241.25   $241.30  
  Purchase #5 $73.54   6.261%   $78.1443   $78.14   $78.15   $78.10  
  Purchase #6 $248.99   7.716%   $268.2021   $268.20   $268.20   $268.20  
  Purchase #7 $6.59   9.431%   $7.2115   $7.21   $7.20   $7.20  
  7 purchase totals = $701.46       $763.8540   $763.84   $763.85   $763.80