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 $140.26   11.655%   $156.6073   $156.61   $156.60   $156.60  
  Purchase #2 $194.39   11.716%   $217.1647   $217.16   $217.15   $217.20  
  Purchase #3 $96.26   4.676%   $100.7611   $100.76   $100.75   $100.80  
  Purchase #4 $236.69   3.147%   $244.1386   $244.14   $244.15   $244.10  
  Purchase #5 $94.43   13.541%   $107.2168   $107.22   $107.20   $107.20  
  Purchase #6 $230.97   10.116%   $254.3349   $254.33   $254.35   $254.30  
  Purchase #7 $23.88   11.642%   $26.6601   $26.66   $26.65   $26.70  
  7 purchase totals = $1,016.88       $1,106.8835   $1,106.88   $1,106.85   $1,106.90