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 $129.91   13.386%   $147.2998   $147.30   $147.30   $147.30  
  Purchase #2 $222.87   10.151%   $245.4935   $245.49   $245.50   $245.50  
  Purchase #3 $179.99   11.622%   $200.9084   $200.91   $200.90   $200.90  
  Purchase #4 $201.73   7.773%   $217.4105   $217.41   $217.40   $217.40  
  Purchase #5 $226.42   3.569%   $234.5009   $234.50   $234.50   $234.50  
  Purchase #6 $148.28   10.462%   $163.7931   $163.79   $163.80   $163.80  
  Purchase #7 $207.47   4.673%   $217.1651   $217.17   $217.15   $217.20  
  7 purchase totals = $1,316.67       $1,426.5713   $1,426.57   $1,426.55   $1,426.60