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	$13.58	12.741%	$15.3102	$15.31	$15.30	$15.30
Purchase #2	$133.63	13.300%	$151.4028	$151.40	$151.40	$151.40
Purchase #3	$160.52	7.368%	$172.3471	$172.35	$172.35	$172.30
Purchase #4	$149.28	11.401%	$166.2994	$166.30	$166.30	$166.30
Purchase #5	$213.56	13.498%	$242.3863	$242.39	$242.40	$242.40
Purchase #6	$51.70	4.255%	$53.8998	$53.90	$53.90	$53.90
Purchase #7	$238.91	12.446%	$268.6447	$268.64	$268.65	$268.60
7 purchase totals =	$961.18		$1,070.2903	$1,070.29	$1,070.30	$1,070.20