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 $48.83   7.321%   $52.4048   $52.40   $52.40   $52.40  
  Purchase #2 $159.66   4.561%   $166.9421   $166.94   $166.95   $166.90  
  Purchase #3 $243.80   5.776%   $257.8819   $257.88   $257.90   $257.90  
  Purchase #4 $240.85   3.329%   $248.8679   $248.87   $248.85   $248.90  
  Purchase #5 $165.47   12.365%   $185.9304   $185.93   $185.95   $185.90  
  Purchase #6 $165.84   5.267%   $174.5748   $174.57   $174.55   $174.60  
  Purchase #7 $142.68   10.465%   $157.6115   $157.61   $157.60   $157.60  
  7 purchase totals = $1,167.13       $1,244.2134   $1,244.20   $1,244.20   $1,244.20