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	$233.94	3.748%	$242.7081	$242.71	$242.70	$242.70
Purchase #2	$59.33	13.780%	$67.5057	$67.51	$67.50	$67.50
Purchase #3	$45.45	13.536%	$51.6021	$51.60	$51.60	$51.60
Purchase #4	$240.70	4.564%	$251.6855	$251.69	$251.70	$251.70
Purchase #5	$53.29	3.640%	$55.2298	$55.23	$55.25	$55.20
Purchase #6	$97.73	12.291%	$109.742	$109.74	$109.75	$109.70
Purchase #7	$188.86	5.137%	$198.5617	$198.56	$198.55	$198.60
7 purchase totals =	$919.30		$977.0349	$977.04	$977.05	$977.00