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	$18.76	9.228%	$20.4912	$20.49	$20.50	$20.50
Purchase #2	$102.65	8.736%	$111.6175	$111.62	$111.60	$111.60
Purchase #3	$193.32	9.695%	$212.0624	$212.06	$212.05	$212.10
Purchase #4	$187.78	11.103%	$208.6292	$208.63	$208.65	$208.60
Purchase #5	$104.32	5.115%	$109.656	$109.66	$109.65	$109.70
Purchase #6	$102.79	13.625%	$116.7951	$116.80	$116.80	$116.80
Purchase #7	$228.29	6.396%	$242.8914	$242.89	$242.90	$242.90
7 purchase totals =	$937.91		$1,022.1428	$1,022.15	$1,022.15	$1,022.20