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	$131.39	9.156%	$143.4201	$143.42	$143.40	$143.40
Purchase #2	$20.78	7.792%	$22.3992	$22.40	$22.40	$22.40
Purchase #3	$167.26	12.684%	$188.4753	$188.48	$188.50	$188.50
Purchase #4	$74.89	5.630%	$79.1063	$79.11	$79.10	$79.10
Purchase #5	$103.51	7.385%	$111.1542	$111.15	$111.15	$111.20
Purchase #6	$46.84	11.319%	$52.1418	$52.14	$52.15	$52.10
Purchase #7	$54.41	11.164%	$60.4843	$60.48	$60.50	$60.50
7 purchase totals =	$599.08		$657.1812	$657.18	$657.20	$657.20