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 $208.89   8.757%   $227.1825   $227.18   $227.20   $227.20  
  Purchase #2 $226.80   12.243%   $254.5671   $254.57   $254.55   $254.60  
  Purchase #3 $223.76   13.190%   $253.2739   $253.27   $253.25   $253.30  
  Purchase #4 $156.68   3.578%   $162.286   $162.29   $162.30   $162.30  
  Purchase #5 $35.26   11.284%   $39.2387   $39.24   $39.25   $39.20  
  Purchase #6 $248.40   12.706%   $279.9617   $279.96   $279.95   $280.00  
  Purchase #7 $109.59   7.808%   $118.1468   $118.15   $118.15   $118.10  
  7 purchase totals = $1,209.38       $1,334.6567   $1,334.66   $1,334.65   $1,334.70