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 $246.94   11.758%   $275.9752   $275.98   $276.00   $276.00  
  Purchase #2 $155.43   6.429%   $165.4226   $165.42   $165.40   $165.40  
  Purchase #3 $48.84   4.346%   $50.9626   $50.96   $50.95   $51.00  
  Purchase #4 $176.74   12.694%   $199.1754   $199.18   $199.20   $199.20  
  Purchase #5 $76.62   10.366%   $84.5624   $84.56   $84.55   $84.60  
  Purchase #6 $215.46   7.189%   $230.9494   $230.95   $230.95   $230.90  
  Purchase #7 $44.45   4.325%   $46.3725   $46.37   $46.35   $46.40  
  7 purchase totals = $964.48       $1,053.4201   $1,053.42   $1,053.40   $1,053.50