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 $48.25   11.582%   $53.8383   $53.84   $53.85   $53.80  
  Purchase #2 $47.95   8.324%   $51.9414   $51.94   $51.95   $51.90  
  Purchase #3 $173.94   12.681%   $195.9973   $196.00   $196.00   $196.00  
  Purchase #4 $44.81   6.726%   $47.8239   $47.82   $47.80   $47.80  
  Purchase #5 $134.89   7.207%   $144.6115   $144.61   $144.60   $144.60  
  Purchase #6 $148.70   11.633%   $165.9983   $166.00   $166.00   $166.00  
  Purchase #7 $154.46   11.300%   $171.914   $171.91   $171.90   $171.90  
  7 purchase totals = $753.00       $832.1247   $832.12   $832.10   $832.00