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 $158.44   11.244%   $176.255   $176.26   $176.25   $176.30  
  Purchase #2 $54.48   8.166%   $58.9288   $58.93   $58.95   $58.90  
  Purchase #3 $99.49   12.785%   $112.2098   $112.21   $112.20   $112.20  
  Purchase #4 $231.98   7.763%   $249.9886   $249.99   $250.00   $250.00  
  Purchase #5 $218.88   4.583%   $228.9113   $228.91   $228.90   $228.90  
  Purchase #6 $155.79   8.230%   $168.6115   $168.61   $168.60   $168.60  
  Purchase #7 $20.97   12.707%   $23.6347   $23.63   $23.65   $23.60  
  7 purchase totals = $940.03       $1,018.5397   $1,018.54   $1,018.55   $1,018.50