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 $167.85   6.756%   $179.1899   $179.19   $179.20   $179.20  
  Purchase #2 $136.82   8.446%   $148.3758   $148.38   $148.40   $148.40  
  Purchase #3 $150.93   10.438%   $166.6841   $166.68   $166.70   $166.70  
  Purchase #4 $182.47   11.659%   $203.7442   $203.74   $203.75   $203.70  
  Purchase #5 $84.94   7.157%   $91.0192   $91.02   $91.00   $91.00  
  Purchase #6 $118.60   5.721%   $125.3851   $125.39   $125.40   $125.40  
  Purchase #7 $114.87   4.233%   $119.7324   $119.73   $119.75   $119.70  
  7 purchase totals = $956.48       $1,034.1307   $1,034.13   $1,034.20   $1,034.10