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	$159.64	7.863%	$172.1925	$172.19	$172.20	$172.20
Purchase #2	$228.86	11.114%	$254.2955	$254.30	$254.30	$254.30
Purchase #3	$232.64	9.405%	$254.5198	$254.52	$254.50	$254.50
Purchase #4	$72.90	4.618%	$76.2665	$76.27	$76.25	$76.30
Purchase #5	$99.84	10.428%	$110.2513	$110.25	$110.25	$110.30
Purchase #6	$171.59	12.438%	$192.9324	$192.93	$192.95	$192.90
Purchase #7	$96.54	3.720%	$100.1313	$100.13	$100.15	$100.10
7 purchase totals =	$1,062.01		$1,160.5893	$1,160.59	$1,160.60	$1,160.60