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 $87.29   11.434%   $97.2707   $97.27   $97.25   $97.30  
  Purchase #2 $91.77   10.599%   $101.4967   $101.50   $101.50   $101.50  
  Purchase #3 $24.72   10.180%   $27.2365   $27.24   $27.25   $27.20  
  Purchase #4 $174.87   4.851%   $183.3529   $183.35   $183.35   $183.40  
  Purchase #5 $184.54   13.247%   $208.986   $208.99   $209.00   $209.00  
  Purchase #6 $242.59   9.571%   $265.8083   $265.81   $265.80   $265.80  
  Purchase #7 $39.72   13.626%   $45.1322   $45.13   $45.15   $45.10  
  7 purchase totals = $845.50       $929.2833   $929.29   $929.30   $929.30