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 $40.62   13.691%   $46.1813   $46.18   $46.20   $46.20  
  Purchase #2 $248.33   6.848%   $265.3356   $265.34   $265.35   $265.30  
  Purchase #3 $235.74   13.732%   $268.1118   $268.11   $268.10   $268.10  
  Purchase #4 $111.75   13.637%   $126.9893   $126.99   $127.00   $127.00  
  Purchase #5 $210.85   3.228%   $217.6562   $217.66   $217.65   $217.70  
  Purchase #6 $10.60   13.433%   $12.0239   $12.02   $12.00   $12.00  
  Purchase #7 $24.57   3.303%   $25.3815   $25.38   $25.40   $25.40  
  7 purchase totals = $882.46       $961.6796   $961.68   $961.70   $961.70