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 $203.58   10.507%   $224.9702   $224.97   $224.95   $225.00  
  Purchase #2 $219.45   13.660%   $249.4269   $249.43   $249.45   $249.40  
  Purchase #3 $235.50   10.837%   $261.0211   $261.02   $261.00   $261.00  
  Purchase #4 $150.97   4.320%   $157.4919   $157.49   $157.50   $157.50  
  Purchase #5 $36.66   8.808%   $39.889   $39.89   $39.90   $39.90  
  Purchase #6 $86.80   9.723%   $95.2396   $95.24   $95.25   $95.20  
  Purchase #7 $215.28   8.337%   $233.2279   $233.23   $233.25   $233.20  
  7 purchase totals = $1,148.24       $1,261.2666   $1,261.27   $1,261.30   $1,261.20