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 $234.84   13.775%   $267.1892   $267.19   $267.20   $267.20  
  Purchase #2 $200.47   8.547%   $217.6042   $217.60   $217.60   $217.60  
  Purchase #3 $58.43   3.269%   $60.3401   $60.34   $60.35   $60.30  
  Purchase #4 $100.68   3.716%   $104.4213   $104.42   $104.40   $104.40  
  Purchase #5 $121.25   9.493%   $132.7603   $132.76   $132.75   $132.80  
  Purchase #6 $167.39   9.467%   $183.2368   $183.24   $183.25   $183.20  
  Purchase #7 $53.41   10.173%   $58.8434   $58.84   $58.85   $58.80  
  7 purchase totals = $936.47       $1,024.3953   $1,024.39   $1,024.40   $1,024.30