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 $126.61   11.637%   $141.3436   $141.34   $141.35   $141.30  
  Purchase #2 $228.72   11.251%   $254.4533   $254.45   $254.45   $254.50  
  Purchase #3 $85.94   11.851%   $96.1247   $96.12   $96.10   $96.10  
  Purchase #4 $141.79   5.388%   $149.4296   $149.43   $149.45   $149.40  
  Purchase #5 $76.44   11.128%   $84.9462   $84.95   $84.95   $84.90  
  Purchase #6 $141.99   12.214%   $159.3327   $159.33   $159.35   $159.30  
  Purchase #7 $112.27   4.661%   $117.5029   $117.50   $117.50   $117.50  
  7 purchase totals = $913.76       $1,003.1330   $1,003.12   $1,003.15   $1,003.00