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 $46.62   3.731%   $48.3594   $48.36   $48.35   $48.40  
  Purchase #2 $246.82   11.650%   $275.5745   $275.57   $275.55   $275.60  
  Purchase #3 $228.68   4.455%   $238.8677   $238.87   $238.85   $238.90  
  Purchase #4 $13.45   12.354%   $15.1116   $15.11   $15.10   $15.10  
  Purchase #5 $187.62   9.459%   $205.367   $205.37   $205.35   $205.40  
  Purchase #6 $148.80   5.792%   $157.4185   $157.42   $157.40   $157.40  
  Purchase #7 $63.97   6.622%   $68.2061   $68.21   $68.20   $68.20  
  7 purchase totals = $935.96       $1,008.9048   $1,008.91   $1,008.80   $1,009.00