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 $52.96   12.237%   $59.4407   $59.44   $59.45   $59.40  
  Purchase #2 $168.58   11.594%   $188.1252   $188.13   $188.15   $188.10  
  Purchase #3 $8.49   13.781%   $9.66   $9.66   $9.65   $9.70  
  Purchase #4 $162.27   11.329%   $180.6536   $180.65   $180.65   $180.70  
  Purchase #5 $72.48   11.645%   $80.9203   $80.92   $80.90   $80.90  
  Purchase #6 $126.95   11.579%   $141.6495   $141.65   $141.65   $141.60  
  Purchase #7 $46.44   3.261%   $47.9544   $47.95   $47.95   $48.00  
  7 purchase totals = $638.17       $708.4037   $708.40   $708.40   $708.40