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 $68.26   11.838%   $76.3406   $76.34   $76.35   $76.30  
  Purchase #2 $219.73   9.642%   $240.9164   $240.92   $240.90   $240.90  
  Purchase #3 $145.53   12.539%   $163.778   $163.78   $163.80   $163.80  
  Purchase #4 $25.36   12.550%   $28.5427   $28.54   $28.55   $28.50  
  Purchase #5 $96.74   11.609%   $107.9705   $107.97   $107.95   $108.00  
  Purchase #6 $208.48   13.492%   $236.6081   $236.61   $236.60   $236.60  
  Purchase #7 $175.32   8.480%   $190.1871   $190.19   $190.20   $190.20  
  7 purchase totals = $939.42       $1,044.3434   $1,044.35   $1,044.35   $1,044.30