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 $80.62   6.340%   $85.7313   $85.73   $85.75   $85.70  
  Purchase #2 $181.83   7.608%   $195.6636   $195.66   $195.65   $195.70  
  Purchase #3 $32.71   11.568%   $36.4939   $36.49   $36.50   $36.50  
  Purchase #4 $6.38   8.388%   $6.9152   $6.92   $6.90   $6.90  
  Purchase #5 $239.33   11.541%   $266.9511   $266.95   $266.95   $267.00  
  Purchase #6 $122.46   6.366%   $130.2558   $130.26   $130.25   $130.30  
  Purchase #7 $174.59   11.728%   $195.0659   $195.07   $195.05   $195.10  
  7 purchase totals = $837.92       $917.0768   $917.08   $917.05   $917.20