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 $87.85   7.568%   $94.4985   $94.50   $94.50   $94.50  
  Purchase #2 $96.51   8.528%   $104.7404   $104.74   $104.75   $104.70  
  Purchase #3 $66.84   5.547%   $70.5476   $70.55   $70.55   $70.50  
  Purchase #4 $151.53   12.863%   $171.0213   $171.02   $171.00   $171.00  
  Purchase #5 $78.89   9.311%   $86.2354   $86.24   $86.25   $86.20  
  Purchase #6 $126.40   7.135%   $135.4186   $135.42   $135.40   $135.40  
  Purchase #7 $80.95   12.707%   $91.2363   $91.24   $91.25   $91.20  
  7 purchase totals = $688.97       $753.6981   $753.71   $753.70   $753.50