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 $207.69   12.804%   $234.2826   $234.28   $234.30   $234.30  
  Purchase #2 $215.57   12.499%   $242.5141   $242.51   $242.50   $242.50  
  Purchase #3 $56.28   10.622%   $62.2581   $62.26   $62.25   $62.30  
  Purchase #4 $169.32   12.732%   $190.8778   $190.88   $190.90   $190.90  
  Purchase #5 $53.47   12.239%   $60.0142   $60.01   $60.00   $60.00  
  Purchase #6 $240.98   5.364%   $253.9062   $253.91   $253.90   $253.90  
  Purchase #7 $237.44   7.487%   $255.2171   $255.22   $255.20   $255.20  
  7 purchase totals = $1,180.75       $1,299.0701   $1,299.07   $1,299.05   $1,299.10