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 $249.64   5.687%   $263.837   $263.84   $263.85   $263.80  
  Purchase #2 $191.32   13.776%   $217.6762   $217.68   $217.70   $217.70  
  Purchase #3 $165.55   12.756%   $186.6676   $186.67   $186.65   $186.70  
  Purchase #4 $154.28   10.125%   $169.9009   $169.90   $169.90   $169.90  
  Purchase #5 $38.39   13.749%   $43.6682   $43.67   $43.65   $43.70  
  Purchase #6 $206.40   13.356%   $233.9668   $233.97   $233.95   $234.00  
  Purchase #7 $164.62   13.296%   $186.5079   $186.51   $186.50   $186.50  
  7 purchase totals = $1,170.20       $1,302.2246   $1,302.24   $1,302.20   $1,302.30