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	$131.59	11.250%	$146.3939	$146.39	$146.40	$146.40
Purchase #2	$65.41	12.690%	$73.7105	$73.71	$73.70	$73.70
Purchase #3	$74.90	11.222%	$83.3053	$83.31	$83.30	$83.30
Purchase #4	$133.73	11.279%	$148.8134	$148.81	$148.80	$148.80
Purchase #5	$232.79	3.585%	$241.1355	$241.14	$241.15	$241.10
Purchase #6	$64.47	9.486%	$70.5856	$70.59	$70.60	$70.60
Purchase #7	$97.99	13.596%	$111.3127	$111.31	$111.30	$111.30
7 purchase totals =	$800.88		$875.2569	$875.26	$875.25	$875.20