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 $83.46   5.398%   $87.9652   $87.97   $87.95   $88.00  
  Purchase #2 $106.81   7.150%   $114.4469   $114.45   $114.45   $114.40  
  Purchase #3 $61.35   4.278%   $63.9746   $63.97   $63.95   $64.00  
  Purchase #4 $234.46   9.133%   $255.8732   $255.87   $255.85   $255.90  
  Purchase #5 $45.46   12.248%   $51.0279   $51.03   $51.05   $51.00  
  Purchase #6 $129.71   11.237%   $144.2855   $144.29   $144.30   $144.30  
  Purchase #7 $245.55   8.337%   $266.0215   $266.02   $266.00   $266.00  
  7 purchase totals = $906.80       $983.5948   $983.60   $983.55   $983.60