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	$62.53	6.350%	$66.5007	$66.50	$66.50	$66.50
Purchase #2	$239.26	11.434%	$266.617	$266.62	$266.60	$266.60
Purchase #3	$99.61	9.754%	$109.326	$109.33	$109.35	$109.30
Purchase #4	$139.42	11.815%	$155.8925	$155.89	$155.90	$155.90
Purchase #5	$111.44	6.433%	$118.6089	$118.61	$118.60	$118.60
Purchase #6	$116.45	12.738%	$131.2834	$131.28	$131.30	$131.30
Purchase #7	$20.84	8.749%	$22.6633	$22.66	$22.65	$22.70
7 purchase totals =	$789.55		$870.8918	$870.89	$870.90	$870.90