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 $187.93   9.241%   $205.2966   $205.30   $205.30   $205.30  
  Purchase #2 $135.57   11.669%   $151.3897   $151.39   $151.40   $151.40  
  Purchase #3 $154.73   9.847%   $169.9663   $169.97   $169.95   $170.00  
  Purchase #4 $61.84   6.623%   $65.9357   $65.94   $65.95   $65.90  
  Purchase #5 $169.41   4.274%   $176.6506   $176.65   $176.65   $176.70  
  Purchase #6 $57.87   9.702%   $63.4845   $63.48   $63.50   $63.50  
  Purchase #7 $44.62   12.397%   $50.1515   $50.15   $50.15   $50.20  
  7 purchase totals = $811.97       $882.8749   $882.88   $882.90   $883.00