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 $79.71   8.247%   $86.2837   $86.28   $86.30   $86.30  
  Purchase #2 $93.92   4.706%   $98.3399   $98.34   $98.35   $98.30  
  Purchase #3 $119.48   3.446%   $123.5973   $123.60   $123.60   $123.60  
  Purchase #4 $118.93   5.114%   $125.0121   $125.01   $125.00   $125.00  
  Purchase #5 $62.93   12.385%   $70.7239   $70.72   $70.70   $70.70  
  Purchase #6 $152.80   3.785%   $158.5835   $158.58   $158.60   $158.60  
  Purchase #7 $234.51   8.653%   $254.8022   $254.80   $254.80   $254.80  
  7 purchase totals = $862.28       $917.3426   $917.33   $917.35   $917.30