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 $60.57   7.778%   $65.2811   $65.28   $65.30   $65.30  
  Purchase #2 $48.81   3.342%   $50.4412   $50.44   $50.45   $50.40  
  Purchase #3 $9.81   9.819%   $10.7732   $10.77   $10.75   $10.80  
  Purchase #4 $211.50   11.667%   $236.1757   $236.18   $236.20   $236.20  
  Purchase #5 $24.60   6.871%   $26.2903   $26.29   $26.30   $26.30  
  Purchase #6 $188.73   8.172%   $204.153   $204.15   $204.15   $204.20  
  Purchase #7 $12.36   5.455%   $13.0342   $13.03   $13.05   $13.00  
  7 purchase totals = $556.38       $606.1487   $606.14   $606.20   $606.20