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 $91.25   6.304%   $97.0024   $97.00   $97.00   $97.00  
  Purchase #2 $191.45   9.506%   $209.6492   $209.65   $209.65   $209.60  
  Purchase #3 $106.72   7.860%   $115.1082   $115.11   $115.10   $115.10  
  Purchase #4 $236.38   10.553%   $261.3252   $261.33   $261.35   $261.30  
  Purchase #5 $24.51   12.604%   $27.5992   $27.60   $27.60   $27.60  
  Purchase #6 $95.71   9.590%   $104.8886   $104.89   $104.90   $104.90  
  Purchase #7 $210.41   3.630%   $218.0479   $218.05   $218.05   $218.00  
  7 purchase totals = $956.43       $1,033.6207   $1,033.63   $1,033.65   $1,033.50