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 $135.69   10.214%   $149.5494   $149.55   $149.55   $149.50  
  Purchase #2 $142.39   11.858%   $159.2746   $159.27   $159.25   $159.30  
  Purchase #3 $171.50   10.439%   $189.4029   $189.40   $189.40   $189.40  
  Purchase #4 $61.71   7.499%   $66.3376   $66.34   $66.35   $66.30  
  Purchase #5 $66.48   5.657%   $70.2408   $70.24   $70.25   $70.20  
  Purchase #6 $64.54   11.708%   $72.0963   $72.10   $72.10   $72.10  
  Purchase #7 $111.79   13.343%   $126.7061   $126.71   $126.70   $126.70  
  7 purchase totals = $754.10       $833.6077   $833.61   $833.60   $833.50