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 $55.97   10.743%   $61.9829   $61.98   $62.00   $62.00  
  Purchase #2 $44.78   7.259%   $48.0306   $48.03   $48.05   $48.00  
  Purchase #3 $54.68   5.785%   $57.8432   $57.84   $57.85   $57.80  
  Purchase #4 $250.74   9.867%   $275.4805   $275.48   $275.50   $275.50  
  Purchase #5 $13.54   5.316%   $14.2598   $14.26   $14.25   $14.30  
  Purchase #6 $134.59   10.745%   $149.0517   $149.05   $149.05   $149.10  
  Purchase #7 $131.74   5.134%   $138.5035   $138.50   $138.50   $138.50  
  7 purchase totals = $686.04       $745.1522   $745.14   $745.20   $745.20