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 $209.51   3.214%   $216.2437   $216.24   $216.25   $216.20  
  Purchase #2 $155.92   11.166%   $173.33   $173.33   $173.35   $173.30  
  Purchase #3 $247.88   5.532%   $261.5927   $261.59   $261.60   $261.60  
  Purchase #4 $67.85   13.258%   $76.8456   $76.85   $76.85   $76.80  
  Purchase #5 $116.37   11.375%   $129.6071   $129.61   $129.60   $129.60  
  Purchase #6 $160.42   10.236%   $176.8406   $176.84   $176.85   $176.80  
  Purchase #7 $6.73   12.243%   $7.554   $7.55   $7.55   $7.60  
  7 purchase totals = $964.68       $1,042.0137   $1,042.01   $1,042.05   $1,041.90