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	$78.74	13.622%	$89.466	$89.47	$89.45	$89.50
Purchase #2	$236.57	13.619%	$268.7885	$268.79	$268.80	$268.80
Purchase #3	$67.28	4.494%	$70.3036	$70.30	$70.30	$70.30
Purchase #4	$89.74	10.564%	$99.2201	$99.22	$99.20	$99.20
Purchase #5	$137.27	13.852%	$156.2846	$156.28	$156.30	$156.30
Purchase #6	$213.29	11.556%	$237.9378	$237.94	$237.95	$237.90
Purchase #7	$137.44	8.123%	$148.6043	$148.60	$148.60	$148.60
7 purchase totals =	$960.33		$1,070.6049	$1,070.60	$1,070.60	$1,070.60