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	$152.69	4.131%	$158.9976	$159.00	$159.00	$159.00
Purchase #2	$219.89	9.109%	$239.9198	$239.92	$239.90	$239.90
Purchase #3	$230.31	10.701%	$254.9555	$254.96	$254.95	$255.00
Purchase #4	$89.38	5.755%	$94.5238	$94.52	$94.50	$94.50
Purchase #5	$243.79	8.427%	$264.3342	$264.33	$264.35	$264.30
Purchase #6	$47.76	3.433%	$49.3996	$49.40	$49.40	$49.40
Purchase #7	$99.74	10.228%	$109.9414	$109.94	$109.95	$109.90
7 purchase totals =	$1,083.56		$1,172.0719	$1,172.07	$1,172.05	$1,172.00