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	$154.97	12.106%	$173.7307	$173.73	$173.75	$173.70
Purchase #2	$207.59	11.843%	$232.1749	$232.17	$232.15	$232.20
Purchase #3	$246.79	3.120%	$254.4898	$254.49	$254.50	$254.50
Purchase #4	$33.32	11.861%	$37.2721	$37.27	$37.25	$37.30
Purchase #5	$6.34	11.614%	$7.0763	$7.08	$7.10	$7.10
Purchase #6	$64.49	12.124%	$72.3088	$72.31	$72.30	$72.30
Purchase #7	$92.65	13.426%	$105.0892	$105.09	$105.10	$105.10
7 purchase totals =	$806.15		$882.1418	$882.14	$882.15	$882.20