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	$123.75	5.207%	$130.1937	$130.19	$130.20	$130.20
Purchase #2	$80.93	10.173%	$89.163	$89.16	$89.15	$89.20
Purchase #3	$124.88	11.738%	$139.5384	$139.54	$139.55	$139.50
Purchase #4	$122.77	8.445%	$133.1379	$133.14	$133.15	$133.10
Purchase #5	$183.55	6.427%	$195.3468	$195.35	$195.35	$195.30
Purchase #6	$86.91	5.178%	$91.4102	$91.41	$91.40	$91.40
Purchase #7	$173.78	9.627%	$190.5098	$190.51	$190.50	$190.50
7 purchase totals =	$896.57		$969.2998	$969.30	$969.30	$969.20