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 $164.41   9.636%   $180.2525   $180.25   $180.25   $180.30  
  Purchase #2 $49.94   12.125%   $55.9952   $56.00   $56.00   $56.00  
  Purchase #3 $153.52   11.868%   $171.7398   $171.74   $171.75   $171.70  
  Purchase #4 $200.61   8.475%   $217.6117   $217.61   $217.60   $217.60  
  Purchase #5 $16.92   8.544%   $18.3656   $18.37   $18.35   $18.40  
  Purchase #6 $152.52   9.818%   $167.4944   $167.49   $167.50   $167.50  
  Purchase #7 $146.59   7.407%   $157.4479   $157.45   $157.45   $157.40  
  7 purchase totals = $884.51       $968.9071   $968.91   $968.90   $968.90