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 $189.93   10.182%   $209.2687   $209.27   $209.25   $209.30  
  Purchase #2 $44.99   11.843%   $50.3182   $50.32   $50.30   $50.30  
  Purchase #3 $177.88   10.136%   $195.9099   $195.91   $195.90   $195.90  
  Purchase #4 $172.76   6.691%   $184.3194   $184.32   $184.30   $184.30  
  Purchase #5 $226.91   12.735%   $255.807   $255.81   $255.80   $255.80  
  Purchase #6 $10.46   12.497%   $11.7672   $11.77   $11.75   $11.80  
  Purchase #7 $43.56   11.581%   $48.6047   $48.60   $48.60   $48.60  
  7 purchase totals = $866.49       $955.9951   $956.00   $955.90   $956.00