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 $76.57   13.658%   $87.0279   $87.03   $87.05   $87.00  
  Purchase #2 $125.79   13.400%   $142.6459   $142.65   $142.65   $142.60  
  Purchase #3 $85.26   13.712%   $96.9509   $96.95   $96.95   $97.00  
  Purchase #4 $236.40   11.271%   $263.0446   $263.04   $263.05   $263.00  
  Purchase #5 $198.28   4.574%   $207.3493   $207.35   $207.35   $207.30  
  Purchase #6 $11.60   11.389%   $12.9211   $12.92   $12.90   $12.90  
  Purchase #7 $51.49   11.348%   $57.3331   $57.33   $57.35   $57.30  
  7 purchase totals = $785.39       $867.2728   $867.27   $867.30   $867.10