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 $86.79   10.692%   $96.0696   $96.07   $96.05   $96.10  
  Purchase #2 $240.75   13.831%   $274.0481   $274.05   $274.05   $274.00  
  Purchase #3 $241.87   7.319%   $259.5725   $259.57   $259.55   $259.60  
  Purchase #4 $183.45   10.828%   $203.314   $203.31   $203.30   $203.30  
  Purchase #5 $62.63   6.508%   $66.706   $66.71   $66.70   $66.70  
  Purchase #6 $70.88   12.459%   $79.7109   $79.71   $79.70   $79.70  
  Purchase #7 $236.55   12.431%   $265.9555   $265.96   $265.95   $266.00  
  7 purchase totals = $1,122.92       $1,245.3766   $1,245.38   $1,245.30   $1,245.40