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	$68.71	13.746%	$78.1549	$78.15	$78.15	$78.20
Purchase #2	$153.89	12.807%	$173.5987	$173.60	$173.60	$173.60
Purchase #3	$40.70	6.272%	$43.2527	$43.25	$43.25	$43.30
Purchase #4	$116.34	5.135%	$122.3141	$122.31	$122.30	$122.30
Purchase #5	$35.74	13.473%	$40.5553	$40.56	$40.55	$40.60
Purchase #6	$230.63	12.433%	$259.3042	$259.30	$259.30	$259.30
Purchase #7	$165.72	5.663%	$175.1047	$175.10	$175.10	$175.10
7 purchase totals =	$811.73		$892.2846	$892.27	$892.25	$892.40