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 $59.39   12.815%   $67.0008   $67.00   $67.00   $67.00  
  Purchase #2 $229.81   6.249%   $244.1708   $244.17   $244.15   $244.20  
  Purchase #3 $163.40   6.421%   $173.8919   $173.89   $173.90   $173.90  
  Purchase #4 $229.58   8.778%   $249.7325   $249.73   $249.75   $249.70  
  Purchase #5 $43.53   10.712%   $48.1929   $48.19   $48.20   $48.20  
  Purchase #6 $217.44   8.670%   $236.292   $236.29   $236.30   $236.30  
  Purchase #7 $206.96   13.244%   $234.3698   $234.37   $234.35   $234.40  
  7 purchase totals = $1,150.11       $1,253.6507   $1,253.64   $1,253.65   $1,253.70