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 $208.97   13.397%   $236.9657   $236.97   $236.95   $237.00  
  Purchase #2 $42.41   13.501%   $48.1358   $48.14   $48.15   $48.10  
  Purchase #3 $62.65   11.498%   $69.8535   $69.85   $69.85   $69.90  
  Purchase #4 $243.28   11.390%   $270.9896   $270.99   $271.00   $271.00  
  Purchase #5 $204.94   10.722%   $226.9137   $226.91   $226.90   $226.90  
  Purchase #6 $244.32   13.287%   $276.7828   $276.78   $276.80   $276.80  
  Purchase #7 $209.47   3.749%   $217.323   $217.32   $217.30   $217.30  
  7 purchase totals = $1,216.04       $1,346.9641   $1,346.96   $1,346.95   $1,347.00