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 $113.50   10.837%   $125.8   $125.80   $125.80   $125.80  
  Purchase #2 $185.45   7.670%   $199.674   $199.67   $199.65   $199.70  
  Purchase #3 $76.50   4.638%   $80.0481   $80.05   $80.05   $80.00  
  Purchase #4 $249.49   4.318%   $260.263   $260.26   $260.25   $260.30  
  Purchase #5 $97.73   10.447%   $107.9399   $107.94   $107.95   $107.90  
  Purchase #6 $122.82   12.823%   $138.5692   $138.57   $138.55   $138.60  
  Purchase #7 $40.43   11.728%   $45.1716   $45.17   $45.15   $45.20  
  7 purchase totals = $885.92       $957.4658   $957.46   $957.40   $957.50