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 $54.62   7.616%   $58.7799   $58.78   $58.80   $58.80  
  Purchase #2 $86.43   8.400%   $93.6901   $93.69   $93.70   $93.70  
  Purchase #3 $50.75   10.130%   $55.891   $55.89   $55.90   $55.90  
  Purchase #4 $162.37   4.492%   $169.6637   $169.66   $169.65   $169.70  
  Purchase #5 $224.30   10.790%   $248.502   $248.50   $248.50   $248.50  
  Purchase #6 $105.60   6.398%   $112.3563   $112.36   $112.35   $112.40  
  Purchase #7 $128.30   9.475%   $140.4564   $140.46   $140.45   $140.50  
  7 purchase totals = $812.37       $879.3394   $879.34   $879.35   $879.50