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 $87.87   6.869%   $93.9058   $93.91   $93.90   $93.90  
  Purchase #2 $155.63   10.795%   $172.4303   $172.43   $172.45   $172.40  
  Purchase #3 $186.73   4.744%   $195.5885   $195.59   $195.60   $195.60  
  Purchase #4 $119.81   9.872%   $131.6376   $131.64   $131.65   $131.60  
  Purchase #5 $146.28   4.645%   $153.0747   $153.07   $153.05   $153.10  
  Purchase #6 $11.84   3.167%   $12.215   $12.22   $12.20   $12.20  
  Purchase #7 $65.49   5.686%   $69.2138   $69.21   $69.20   $69.20  
  7 purchase totals = $773.65       $828.0657   $828.07   $828.05   $828.00