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 $82.36   11.506%   $91.8363   $91.84   $91.85   $91.80  
  Purchase #2 $49.30   9.527%   $53.9968   $54.00   $54.00   $54.00  
  Purchase #3 $109.95   11.322%   $122.3985   $122.40   $122.40   $122.40  
  Purchase #4 $224.48   11.344%   $249.945   $249.95   $249.95   $249.90  
  Purchase #5 $120.25   11.224%   $133.7469   $133.75   $133.75   $133.70  
  Purchase #6 $96.71   8.145%   $104.587   $104.59   $104.60   $104.60  
  Purchase #7 $72.80   5.369%   $76.7086   $76.71   $76.70   $76.70  
  7 purchase totals = $755.85       $833.2191   $833.24   $833.25   $833.10