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 $49.95   11.162%   $55.5254   $55.53   $55.55   $55.50  
  Purchase #2 $10.46   8.380%   $11.3365   $11.34   $11.35   $11.30  
  Purchase #3 $225.50   13.356%   $255.6178   $255.62   $255.60   $255.60  
  Purchase #4 $250.93   5.502%   $264.7362   $264.74   $264.75   $264.70  
  Purchase #5 $249.84   4.800%   $261.8323   $261.83   $261.85   $261.80  
  Purchase #6 $60.51   12.269%   $67.934   $67.93   $67.95   $67.90  
  Purchase #7 $233.83   4.425%   $244.177   $244.18   $244.20   $244.20  
  7 purchase totals = $1,081.02       $1,161.1592   $1,161.17   $1,161.25   $1,161.00