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	$83.52	7.161%	$89.5009	$89.50	$89.50	$89.50
Purchase #2	$198.25	5.735%	$209.6196	$209.62	$209.60	$209.60
Purchase #3	$215.84	9.301%	$235.9153	$235.92	$235.90	$235.90
Purchase #4	$99.49	10.592%	$110.028	$110.03	$110.05	$110.00
Purchase #5	$148.33	4.825%	$155.4869	$155.49	$155.50	$155.50
Purchase #6	$108.37	9.715%	$118.8981	$118.90	$118.90	$118.90
Purchase #7	$112.66	3.701%	$116.8295	$116.83	$116.85	$116.80
7 purchase totals =	$966.46		$1,036.2783	$1,036.29	$1,036.30	$1,036.20