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 $195.98   7.674%   $211.0195   $211.02   $211.00   $211.00  
  Purchase #2 $123.86   12.176%   $138.9412   $138.94   $138.95   $138.90  
  Purchase #3 $176.44   7.463%   $189.6077   $189.61   $189.60   $189.60  
  Purchase #4 $54.31   8.449%   $58.8987   $58.90   $58.90   $58.90  
  Purchase #5 $246.75   11.272%   $274.5637   $274.56   $274.55   $274.60  
  Purchase #6 $52.77   10.494%   $58.3077   $58.31   $58.30   $58.30  
  Purchase #7 $30.76   4.645%   $32.1888   $32.19   $32.20   $32.20  
  7 purchase totals = $880.87       $963.5273   $963.53   $963.50   $963.50