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 $63.71   8.768%   $69.2961   $69.30   $69.30   $69.30  
  Purchase #2 $123.99   9.730%   $136.0542   $136.05   $136.05   $136.10  
  Purchase #3 $151.98   11.308%   $169.1659   $169.17   $169.15   $169.20  
  Purchase #4 $242.63   6.619%   $258.6897   $258.69   $258.70   $258.70  
  Purchase #5 $98.58   6.369%   $104.8586   $104.86   $104.85   $104.90  
  Purchase #6 $39.60   5.120%   $41.6275   $41.63   $41.65   $41.60  
  Purchase #7 $75.64   6.566%   $80.6065   $80.61   $80.60   $80.60  
  7 purchase totals = $796.13       $860.2985   $860.31   $860.30   $860.40