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 $216.70   12.566%   $243.9305   $243.93   $243.95   $243.90  
  Purchase #2 $157.66   11.796%   $176.2576   $176.26   $176.25   $176.30  
  Purchase #3 $146.92   10.334%   $162.1027   $162.10   $162.10   $162.10  
  Purchase #4 $114.28   13.407%   $129.6015   $129.60   $129.60   $129.60  
  Purchase #5 $84.50   5.541%   $89.1821   $89.18   $89.20   $89.20  
  Purchase #6 $19.61   13.301%   $22.2183   $22.22   $22.20   $22.20  
  Purchase #7 $170.28   12.469%   $191.5122   $191.51   $191.50   $191.50  
  7 purchase totals = $909.95       $1,014.8049   $1,014.80   $1,014.80   $1,014.80