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 $63.48   3.228%   $65.5291   $65.53   $65.55   $65.50  
  Purchase #2 $245.30   12.829%   $276.7695   $276.77   $276.75   $276.80  
  Purchase #3 $93.95   4.462%   $98.142   $98.14   $98.15   $98.10  
  Purchase #4 $211.30   10.274%   $233.009   $233.01   $233.00   $233.00  
  Purchase #5 $33.46   10.487%   $36.969   $36.97   $36.95   $37.00  
  Purchase #6 $115.88   7.846%   $124.9719   $124.97   $124.95   $125.00  
  Purchase #7 $73.54   11.428%   $81.9442   $81.94   $81.95   $81.90  
  7 purchase totals = $836.91       $917.3347   $917.33   $917.30   $917.30