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 $93.43   5.362%   $98.4397   $98.44   $98.45   $98.40  
  Purchase #2 $52.99   6.802%   $56.5944   $56.59   $56.60   $56.60  
  Purchase #3 $157.47   11.584%   $175.7113   $175.71   $175.70   $175.70  
  Purchase #4 $234.75   9.206%   $256.3611   $256.36   $256.35   $256.40  
  Purchase #5 $154.70   5.716%   $163.5427   $163.54   $163.55   $163.50  
  Purchase #6 $210.85   12.762%   $237.7587   $237.76   $237.75   $237.80  
  Purchase #7 $24.55   11.804%   $27.4479   $27.45   $27.45   $27.40  
  7 purchase totals = $928.74       $1,015.8558   $1,015.85   $1,015.85   $1,015.80