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 $75.26   12.690%   $84.8105   $84.81   $84.80   $84.80  
  Purchase #2 $60.41   5.186%   $63.5429   $63.54   $63.55   $63.50  
  Purchase #3 $162.63   11.223%   $180.882   $180.88   $180.90   $180.90  
  Purchase #4 $216.55   13.623%   $246.0506   $246.05   $246.05   $246.10  
  Purchase #5 $242.26   13.262%   $274.3885   $274.39   $274.40   $274.40  
  Purchase #6 $101.39   10.521%   $112.0572   $112.06   $112.05   $112.10  
  Purchase #7 $125.74   7.511%   $135.1843   $135.18   $135.20   $135.20  
  7 purchase totals = $984.24       $1,096.9160   $1,096.91   $1,096.95   $1,097.00