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	$138.76	13.208%	$157.0874	$157.09	$157.10	$157.10
Purchase #2	$158.73	9.196%	$173.3268	$173.33	$173.35	$173.30
Purchase #3	$25.82	9.736%	$28.3338	$28.33	$28.35	$28.30
Purchase #4	$87.61	13.811%	$99.7098	$99.71	$99.70	$99.70
Purchase #5	$226.98	10.848%	$251.6028	$251.60	$251.60	$251.60
Purchase #6	$188.86	3.253%	$195.0036	$195.00	$195.00	$195.00
Purchase #7	$73.55	6.615%	$78.4153	$78.42	$78.40	$78.40
7 purchase totals =	$900.31		$983.4795	$983.48	$983.50	$983.40