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	$229.46	4.309%	$239.3474	$239.35	$239.35	$239.30
Purchase #2	$199.89	12.659%	$225.1941	$225.19	$225.20	$225.20
Purchase #3	$12.26	7.348%	$13.1609	$13.16	$13.15	$13.20
Purchase #4	$168.83	11.633%	$188.47	$188.47	$188.45	$188.50
Purchase #5	$151.72	11.640%	$169.3802	$169.38	$169.40	$169.40
Purchase #6	$179.38	9.448%	$196.3278	$196.33	$196.35	$196.30
Purchase #7	$195.38	7.853%	$210.7232	$210.72	$210.70	$210.70
7 purchase totals =	$1,136.92		$1,242.6036	$1,242.60	$1,242.60	$1,242.60