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 $57.98   4.788%   $60.7561   $60.76   $60.75   $60.80  
  Purchase #2 $52.74   10.491%   $58.273   $58.27   $58.25   $58.30  
  Purchase #3 $116.53   11.460%   $129.8843   $129.88   $129.90   $129.90  
  Purchase #4 $233.35   13.276%   $264.3295   $264.33   $264.35   $264.30  
  Purchase #5 $77.66   10.475%   $85.7949   $85.79   $85.80   $85.80  
  Purchase #6 $154.78   12.355%   $173.9031   $173.90   $173.90   $173.90  
  Purchase #7 $239.64   4.762%   $251.0517   $251.05   $251.05   $251.10  
  7 purchase totals = $932.68       $1,023.9926   $1,023.98   $1,024.00   $1,024.10