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	$188.47	11.753%	$210.6209	$210.62	$210.60	$210.60
Purchase #2	$232.89	9.573%	$255.1846	$255.18	$255.20	$255.20
Purchase #3	$141.52	13.620%	$160.795	$160.80	$160.80	$160.80
Purchase #4	$202.40	13.247%	$229.2119	$229.21	$229.20	$229.20
Purchase #5	$179.87	3.573%	$186.2968	$186.30	$186.30	$186.30
Purchase #6	$39.53	9.592%	$43.3217	$43.32	$43.30	$43.30
Purchase #7	$157.86	7.537%	$169.7579	$169.76	$169.75	$169.80
7 purchase totals =	$1,142.54		$1,255.1888	$1,255.19	$1,255.15	$1,255.20