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 $248.77   10.539%   $274.9879   $274.99   $275.00   $275.00  
  Purchase #2 $186.31   4.426%   $194.5561   $194.56   $194.55   $194.60  
  Purchase #3 $224.41   9.436%   $245.5853   $245.59   $245.60   $245.60  
  Purchase #4 $138.26   9.321%   $151.1472   $151.15   $151.15   $151.10  
  Purchase #5 $211.73   11.699%   $236.5003   $236.50   $236.50   $236.50  
  Purchase #6 $175.31   9.283%   $191.584   $191.58   $191.60   $191.60  
  Purchase #7 $158.49   11.646%   $176.9477   $176.95   $176.95   $176.90  
  7 purchase totals = $1,343.28       $1,471.3085   $1,471.32   $1,471.35   $1,471.30