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 $57.53   12.117%   $64.5009   $64.50   $64.50   $64.50  
  Purchase #2 $69.43   4.754%   $72.7307   $72.73   $72.75   $72.70  
  Purchase #3 $212.27   4.341%   $221.4846   $221.48   $221.50   $221.50  
  Purchase #4 $86.96   11.174%   $96.6769   $96.68   $96.70   $96.70  
  Purchase #5 $74.72   9.394%   $81.7392   $81.74   $81.75   $81.70  
  Purchase #6 $53.81   9.593%   $58.972   $58.97   $58.95   $59.00  
  Purchase #7 $247.48   4.442%   $258.4731   $258.47   $258.45   $258.50  
  7 purchase totals = $802.20       $854.5774   $854.57   $854.60   $854.60