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 $70.58   3.483%   $73.0383   $73.04   $73.05   $73.00  
  Purchase #2 $121.70   3.204%   $125.5993   $125.60   $125.60   $125.60  
  Purchase #3 $216.76   11.827%   $242.3962   $242.40   $242.40   $242.40  
  Purchase #4 $101.39   13.211%   $114.7846   $114.78   $114.80   $114.80  
  Purchase #5 $171.76   5.703%   $181.5555   $181.56   $181.55   $181.60  
  Purchase #6 $55.86   3.282%   $57.6933   $57.69   $57.70   $57.70  
  Purchase #7 $51.68   5.728%   $54.6402   $54.64   $54.65   $54.60  
  7 purchase totals = $789.73       $849.7074   $849.71   $849.75   $849.70