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	$55.52	4.147%	$57.8224	$57.82	$57.80	$57.80
Purchase #2	$159.56	10.783%	$176.7654	$176.77	$176.75	$176.80
Purchase #3	$31.69	8.309%	$34.3231	$34.32	$34.30	$34.30
Purchase #4	$119.81	6.200%	$127.2382	$127.24	$127.25	$127.20
Purchase #5	$118.92	3.531%	$123.1191	$123.12	$123.10	$123.10
Purchase #6	$199.35	12.290%	$223.8501	$223.85	$223.85	$223.90
Purchase #7	$56.63	12.404%	$63.6544	$63.65	$63.65	$63.70
7 purchase totals =	$741.48		$806.7727	$806.77	$806.70	$806.80