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 $212.92   9.781%   $233.7457   $233.75   $233.75   $233.70  
  Purchase #2 $41.85   10.502%   $46.2451   $46.25   $46.25   $46.20  
  Purchase #3 $193.84   7.579%   $208.5311   $208.53   $208.55   $208.50  
  Purchase #4 $72.78   6.306%   $77.3695   $77.37   $77.35   $77.40  
  Purchase #5 $149.29   13.438%   $169.3516   $169.35   $169.35   $169.40  
  Purchase #6 $125.63   5.647%   $132.7243   $132.72   $132.70   $132.70  
  Purchase #7 $248.38   4.627%   $259.8725   $259.87   $259.85   $259.90  
  7 purchase totals = $1,044.69       $1,127.8398   $1,127.84   $1,127.80   $1,127.80