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 $188.34   8.319%   $204.008   $204.01   $204.00   $204.00  
  Purchase #2 $89.84   6.796%   $95.9455   $95.95   $95.95   $95.90  
  Purchase #3 $214.78   10.169%   $236.621   $236.62   $236.60   $236.60  
  Purchase #4 $191.34   10.245%   $210.9428   $210.94   $210.95   $210.90  
  Purchase #5 $218.84   5.861%   $231.6662   $231.67   $231.65   $231.70  
  Purchase #6 $232.99   3.827%   $241.9065   $241.91   $241.90   $241.90  
  Purchase #7 $78.95   6.177%   $83.8267   $83.83   $83.85   $83.80  
  7 purchase totals = $1,215.08       $1,304.9167   $1,304.93   $1,304.90   $1,304.80