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 $235.28   6.185%   $249.8321   $249.83   $249.85   $249.80  
  Purchase #2 $212.30   12.692%   $239.2451   $239.25   $239.25   $239.20  
  Purchase #3 $57.27   11.610%   $63.919   $63.92   $63.90   $63.90  
  Purchase #4 $243.67   7.627%   $262.2547   $262.25   $262.25   $262.30  
  Purchase #5 $82.47   7.510%   $88.6635   $88.66   $88.65   $88.70  
  Purchase #6 $237.43   3.362%   $245.4124   $245.41   $245.40   $245.40  
  Purchase #7 $132.71   8.285%   $143.705   $143.71   $143.70   $143.70  
  7 purchase totals = $1,201.13       $1,293.0318   $1,293.03   $1,293.00   $1,293.00