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 $55.58   3.872%   $57.7321   $57.73   $57.75   $57.70  
  Purchase #2 $248.85   11.230%   $276.7959   $276.80   $276.80   $276.80  
  Purchase #3 $101.88   13.573%   $115.7082   $115.71   $115.70   $115.70  
  Purchase #4 $155.34   6.376%   $165.2445   $165.24   $165.25   $165.20  
  Purchase #5 $197.97   5.856%   $209.5631   $209.56   $209.55   $209.60  
  Purchase #6 $59.50   4.151%   $61.9698   $61.97   $61.95   $62.00  
  Purchase #7 $127.89   6.249%   $135.8818   $135.88   $135.90   $135.90  
  7 purchase totals = $947.01       $1,022.8954   $1,022.89   $1,022.90   $1,022.90