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 $227.71   7.752%   $245.3621   $245.36   $245.35   $245.40  
  Purchase #2 $23.58   6.646%   $25.1471   $25.15   $25.15   $25.10  
  Purchase #3 $166.92   11.388%   $185.9288   $185.93   $185.95   $185.90  
  Purchase #4 $225.26   4.861%   $236.2099   $236.21   $236.20   $236.20  
  Purchase #5 $41.32   3.537%   $42.7815   $42.78   $42.80   $42.80  
  Purchase #6 $244.94   6.553%   $260.9909   $260.99   $261.00   $261.00  
  Purchase #7 $64.60   6.765%   $68.9702   $68.97   $68.95   $69.00  
  7 purchase totals = $994.33       $1,065.3905   $1,065.39   $1,065.40   $1,065.40