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 $62.37   6.106%   $66.1783   $66.18   $66.20   $66.20  
  Purchase #2 $238.79   8.687%   $259.5337   $259.53   $259.55   $259.50  
  Purchase #3 $125.48   5.327%   $132.1643   $132.16   $132.15   $132.20  
  Purchase #4 $158.55   10.160%   $174.6587   $174.66   $174.65   $174.70  
  Purchase #5 $177.75   7.150%   $190.4591   $190.46   $190.45   $190.50  
  Purchase #6 $22.30   4.827%   $23.3764   $23.38   $23.40   $23.40  
  Purchase #7 $16.51   7.287%   $17.7131   $17.71   $17.70   $17.70  
  7 purchase totals = $801.75       $864.0836   $864.08   $864.10   $864.20