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 $205.57   9.354%   $224.799   $224.80   $224.80   $224.80  
  Purchase #2 $44.72   4.275%   $46.6318   $46.63   $46.65   $46.60  
  Purchase #3 $214.58   4.468%   $224.1674   $224.17   $224.15   $224.20  
  Purchase #4 $65.27   6.826%   $69.7253   $69.73   $69.75   $69.70  
  Purchase #5 $82.26   6.214%   $87.3716   $87.37   $87.35   $87.40  
  Purchase #6 $21.80   11.547%   $24.3172   $24.32   $24.30   $24.30  
  Purchase #7 $58.85   13.202%   $66.6194   $66.62   $66.60   $66.60  
  7 purchase totals = $693.05       $743.6317   $743.64   $743.60   $743.60