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	$100.53	11.714%	$112.3061	$112.31	$112.30	$112.30
Purchase #2	$194.83	11.277%	$216.801	$216.80	$216.80	$216.80
Purchase #3	$232.54	11.715%	$259.7821	$259.78	$259.80	$259.80
Purchase #4	$114.94	13.257%	$130.1776	$130.18	$130.20	$130.20
Purchase #5	$174.77	12.237%	$196.1566	$196.16	$196.15	$196.20
Purchase #6	$147.70	13.704%	$167.9408	$167.94	$167.95	$167.90
Purchase #7	$246.99	5.150%	$259.71	$259.71	$259.70	$259.70
7 purchase totals =	$1,212.30		$1,342.8742	$1,342.88	$1,342.90	$1,342.90