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 $13.94   3.588%   $14.4402   $14.44   $14.45   $14.40  
  Purchase #2 $32.65   9.272%   $35.6773   $35.68   $35.70   $35.70  
  Purchase #3 $95.48   8.474%   $103.571   $103.57   $103.55   $103.60  
  Purchase #4 $18.36   13.714%   $20.8779   $20.88   $20.90   $20.90  
  Purchase #5 $47.94   9.439%   $52.4651   $52.47   $52.45   $52.50  
  Purchase #6 $157.98   7.373%   $169.6279   $169.63   $169.65   $169.60  
  Purchase #7 $206.82   13.125%   $233.9651   $233.97   $233.95   $234.00  
  7 purchase totals = $573.17       $630.6245   $630.64   $630.65   $630.70