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 $224.74   13.701%   $255.5316   $255.53   $255.55   $255.50  
  Purchase #2 $105.85   13.150%   $119.7693   $119.77   $119.75   $119.80  
  Purchase #3 $121.72   3.770%   $126.3088   $126.31   $126.30   $126.30  
  Purchase #4 $211.87   12.157%   $237.627   $237.63   $237.65   $237.60  
  Purchase #5 $232.28   13.787%   $264.3044   $264.30   $264.30   $264.30  
  Purchase #6 $159.46   12.790%   $179.8549   $179.85   $179.85   $179.90  
  Purchase #7 $145.34   13.367%   $164.7676   $164.77   $164.75   $164.80  
  7 purchase totals = $1,201.26       $1,348.1636   $1,348.16   $1,348.15   $1,348.20