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	$10.76	9.764%	$11.8106	$11.81	$11.80	$11.80
Purchase #2	$95.49	11.533%	$106.5029	$106.50	$106.50	$106.50
Purchase #3	$55.86	11.574%	$62.3252	$62.33	$62.35	$62.30
Purchase #4	$40.85	4.687%	$42.7646	$42.76	$42.75	$42.80
Purchase #5	$147.46	5.374%	$155.3845	$155.38	$155.40	$155.40
Purchase #6	$29.58	9.635%	$32.43	$32.43	$32.45	$32.40
Purchase #7	$244.48	4.294%	$254.978	$254.98	$255.00	$255.00
7 purchase totals =	$624.48		$666.1958	$666.19	$666.25	$666.20