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 $61.46   8.254%   $66.5329   $66.53   $66.55   $66.50  
  Purchase #2 $189.85   8.219%   $205.4538   $205.45   $205.45   $205.50  
  Purchase #3 $5.38   10.431%   $5.9412   $5.94   $5.95   $5.90  
  Purchase #4 $102.75   7.108%   $110.0535   $110.05   $110.05   $110.10  
  Purchase #5 $118.37   5.857%   $125.3029   $125.30   $125.30   $125.30  
  Purchase #6 $141.50   7.534%   $152.1606   $152.16   $152.15   $152.20  
  Purchase #7 $101.48   10.861%   $112.5017   $112.50   $112.50   $112.50  
  7 purchase totals = $720.79       $777.9466   $777.93   $777.95   $778.00