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 $39.46   13.803%   $44.9067   $44.91   $44.90   $44.90  
  Purchase #2 $191.47   10.646%   $211.8539   $211.85   $211.85   $211.90  
  Purchase #3 $62.42   7.287%   $66.9685   $66.97   $66.95   $67.00  
  Purchase #4 $109.89   8.505%   $119.2361   $119.24   $119.25   $119.20  
  Purchase #5 $208.58   7.535%   $224.2965   $224.30   $224.30   $224.30  
  Purchase #6 $246.28   13.703%   $280.0277   $280.03   $280.05   $280.00  
  Purchase #7 $12.87   13.573%   $14.6168   $14.62   $14.60   $14.60  
  7 purchase totals = $870.97       $961.9062   $961.92   $961.90   $961.90