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 $220.67   4.789%   $231.2379   $231.24   $231.25   $231.20  
  Purchase #2 $157.39   11.165%   $174.9626   $174.96   $174.95   $175.00  
  Purchase #3 $217.62   6.152%   $231.008   $231.01   $231.00   $231.00  
  Purchase #4 $43.41   8.830%   $47.2431   $47.24   $47.25   $47.20  
  Purchase #5 $233.33   11.392%   $259.911   $259.91   $259.90   $259.90  
  Purchase #6 $209.73   11.484%   $233.8154   $233.82   $233.80   $233.80  
  Purchase #7 $173.87   10.184%   $191.5769   $191.58   $191.60   $191.60  
  7 purchase totals = $1,256.02       $1,369.7549   $1,369.76   $1,369.75   $1,369.70