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 $236.26   5.834%   $250.0434   $250.04   $250.05   $250.00  
  Purchase #2 $206.96   8.671%   $224.9055   $224.91   $224.90   $224.90  
  Purchase #3 $80.83   6.767%   $86.2998   $86.30   $86.30   $86.30  
  Purchase #4 $212.34   6.247%   $225.6049   $225.60   $225.60   $225.60  
  Purchase #5 $148.66   13.772%   $169.1335   $169.13   $169.15   $169.10  
  Purchase #6 $221.76   8.835%   $241.3525   $241.35   $241.35   $241.40  
  Purchase #7 $84.32   11.683%   $94.1711   $94.17   $94.15   $94.20  
  7 purchase totals = $1,191.13       $1,291.5107   $1,291.50   $1,291.50   $1,291.50