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 $213.87   13.264%   $242.2377   $242.24   $242.25   $242.20  
  Purchase #2 $226.38   13.856%   $257.7472   $257.75   $257.75   $257.70  
  Purchase #3 $41.87   4.506%   $43.7567   $43.76   $43.75   $43.80  
  Purchase #4 $14.35   9.271%   $15.6804   $15.68   $15.70   $15.70  
  Purchase #5 $175.91   7.388%   $188.9062   $188.91   $188.90   $188.90  
  Purchase #6 $109.37   7.168%   $117.2096   $117.21   $117.20   $117.20  
  Purchase #7 $151.54   11.502%   $168.9701   $168.97   $168.95   $169.00  
  7 purchase totals = $933.29       $1,034.5079   $1,034.52   $1,034.50   $1,034.50