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 $23.35   13.330%   $26.4626   $26.46   $26.45   $26.50  
  Purchase #2 $142.36   6.598%   $151.7529   $151.75   $151.75   $151.80  
  Purchase #3 $62.79   5.317%   $66.1285   $66.13   $66.15   $66.10  
  Purchase #4 $197.77   9.581%   $216.7183   $216.72   $216.70   $216.70  
  Purchase #5 $165.76   9.314%   $181.1989   $181.20   $181.20   $181.20  
  Purchase #6 $155.78   13.295%   $176.491   $176.49   $176.50   $176.50  
  Purchase #7 $14.46   12.410%   $16.2545   $16.25   $16.25   $16.30  
  7 purchase totals = $762.27       $835.0067   $835.00   $835.00   $835.10