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	$9.96	13.627%	$11.3172	$11.32	$11.30	$11.30
Purchase #2	$22.49	11.340%	$25.0404	$25.04	$25.05	$25.00
Purchase #3	$45.29	12.344%	$50.8806	$50.88	$50.90	$50.90
Purchase #4	$67.64	8.143%	$73.1479	$73.15	$73.15	$73.10
Purchase #5	$95.61	10.357%	$105.5123	$105.51	$105.50	$105.50
Purchase #6	$72.91	6.428%	$77.5967	$77.60	$77.60	$77.60
Purchase #7	$185.71	10.700%	$205.581	$205.58	$205.60	$205.60
7 purchase totals =	$499.61		$549.0761	$549.08	$549.10	$549.00