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 $180.76   5.829%   $191.2965   $191.30   $191.30   $191.30  
  Purchase #2 $24.62   8.441%   $26.6982   $26.70   $26.70   $26.70  
  Purchase #3 $41.45   8.792%   $45.0943   $45.09   $45.10   $45.10  
  Purchase #4 $91.43   8.741%   $99.4219   $99.42   $99.40   $99.40  
  Purchase #5 $130.88   13.236%   $148.2033   $148.20   $148.20   $148.20  
  Purchase #6 $205.84   4.161%   $214.405   $214.41   $214.40   $214.40  
  Purchase #7 $87.69   12.659%   $98.7907   $98.79   $98.80   $98.80  
  7 purchase totals = $762.67       $823.9099   $823.91   $823.90   $823.90