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	$235.89	5.274%	$248.3308	$248.33	$248.35	$248.30
Purchase #2	$151.55	10.865%	$168.0159	$168.02	$168.00	$168.00
Purchase #3	$107.38	5.103%	$112.8596	$112.86	$112.85	$112.90
Purchase #4	$77.73	13.324%	$88.0867	$88.09	$88.10	$88.10
Purchase #5	$159.64	7.580%	$171.7407	$171.74	$171.75	$171.70
Purchase #6	$92.53	3.839%	$96.0822	$96.08	$96.10	$96.10
Purchase #7	$95.89	3.729%	$99.4657	$99.47	$99.45	$99.50
7 purchase totals =	$920.61		$984.5816	$984.59	$984.60	$984.60