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 $235.53   11.522%   $262.6678   $262.67   $262.65   $262.70  
  Purchase #2 $58.56   13.354%   $66.3801   $66.38   $66.40   $66.40  
  Purchase #3 $93.60   8.736%   $101.7769   $101.78   $101.80   $101.80  
  Purchase #4 $205.46   11.874%   $229.8563   $229.86   $229.85   $229.90  
  Purchase #5 $165.34   11.385%   $184.164   $184.16   $184.15   $184.20  
  Purchase #6 $142.82   13.391%   $161.945   $161.95   $161.95   $161.90  
  Purchase #7 $207.65   9.240%   $226.8369   $226.84   $226.85   $226.80  
  7 purchase totals = $1,108.96       $1,233.6270   $1,233.64   $1,233.65   $1,233.70