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 $221.98   6.857%   $237.2012   $237.20   $237.20   $237.20  
  Purchase #2 $66.26   10.395%   $73.1477   $73.15   $73.15   $73.10  
  Purchase #3 $226.96   9.250%   $247.9538   $247.95   $247.95   $248.00  
  Purchase #4 $61.92   3.389%   $64.0185   $64.02   $64.00   $64.00  
  Purchase #5 $174.25   10.339%   $192.2657   $192.27   $192.25   $192.30  
  Purchase #6 $116.29   11.827%   $130.0436   $130.04   $130.05   $130.00  
  Purchase #7 $75.63   12.780%   $85.2955   $85.30   $85.30   $85.30  
  7 purchase totals = $943.29       $1,029.9260   $1,029.93   $1,029.90   $1,029.90