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 $55.25   9.763%   $60.6441   $60.64   $60.65   $60.60  
  Purchase #2 $173.33   8.109%   $187.3853   $187.39   $187.40   $187.40  
  Purchase #3 $114.46   6.141%   $121.489   $121.49   $121.50   $121.50  
  Purchase #4 $203.75   3.351%   $210.5777   $210.58   $210.60   $210.60  
  Purchase #5 $43.43   9.692%   $47.6392   $47.64   $47.65   $47.60  
  Purchase #6 $91.44   13.113%   $103.4305   $103.43   $103.45   $103.40  
  Purchase #7 $58.68   9.340%   $64.1607   $64.16   $64.15   $64.20  
  7 purchase totals = $740.34       $795.3265   $795.33   $795.40   $795.30