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	$127.89	8.428%	$138.6686	$138.67	$138.65	$138.70
Purchase #2	$192.51	7.489%	$206.9271	$206.93	$206.95	$206.90
Purchase #3	$96.47	4.383%	$100.6983	$100.70	$100.70	$100.70
Purchase #4	$26.62	11.811%	$29.7641	$29.76	$29.75	$29.80
Purchase #5	$177.41	10.809%	$196.5862	$196.59	$196.60	$196.60
Purchase #6	$31.42	3.143%	$32.4075	$32.41	$32.40	$32.40
Purchase #7	$153.90	12.166%	$172.6235	$172.62	$172.60	$172.60
7 purchase totals =	$806.22		$877.6753	$877.68	$877.65	$877.70