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 $68.31   12.480%   $76.8351   $76.84   $76.85   $76.80  
  Purchase #2 $100.65   3.622%   $104.2955   $104.30   $104.30   $104.30  
  Purchase #3 $201.71   7.738%   $217.3183   $217.32   $217.30   $217.30  
  Purchase #4 $237.70   12.456%   $267.3079   $267.31   $267.30   $267.30  
  Purchase #5 $88.47   5.141%   $93.0182   $93.02   $93.00   $93.00  
  Purchase #6 $174.95   5.673%   $184.8749   $184.87   $184.85   $184.90  
  Purchase #7 $168.62   11.571%   $188.131   $188.13   $188.15   $188.10  
  7 purchase totals = $1,040.41       $1,131.7809   $1,131.79   $1,131.75   $1,131.70