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 $82.29   13.341%   $93.2683   $93.27   $93.25   $93.30  
  Purchase #2 $200.44   8.377%   $217.2309   $217.23   $217.25   $217.20  
  Purchase #3 $192.38   3.860%   $199.8059   $199.81   $199.80   $199.80  
  Purchase #4 $182.60   13.330%   $206.9406   $206.94   $206.95   $206.90  
  Purchase #5 $20.57   10.221%   $22.6725   $22.67   $22.65   $22.70  
  Purchase #6 $232.58   10.215%   $256.338   $256.34   $256.35   $256.30  
  Purchase #7 $102.65   13.340%   $116.3435   $116.34   $116.35   $116.30  
  7 purchase totals = $1,013.51       $1,112.5997   $1,112.60   $1,112.60   $1,112.50