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 $73.82   3.350%   $76.293   $76.29   $76.30   $76.30  
  Purchase #2 $16.72   4.554%   $17.4814   $17.48   $17.50   $17.50  
  Purchase #3 $36.33   11.578%   $40.5363   $40.54   $40.55   $40.50  
  Purchase #4 $189.34   9.827%   $207.9464   $207.95   $207.95   $207.90  
  Purchase #5 $196.86   9.347%   $215.2605   $215.26   $215.25   $215.30  
  Purchase #6 $227.25   13.586%   $258.1242   $258.12   $258.10   $258.10  
  Purchase #7 $94.76   10.400%   $104.615   $104.62   $104.60   $104.60  
  7 purchase totals = $835.08       $920.2568   $920.26   $920.25   $920.20