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	$22.84	11.559%	$25.4801	$25.48	$25.50	$25.50
Purchase #2	$43.86	4.544%	$45.853	$45.85	$45.85	$45.90
Purchase #3	$242.71	10.707%	$268.697	$268.70	$268.70	$268.70
Purchase #4	$145.70	3.396%	$150.648	$150.65	$150.65	$150.60
Purchase #5	$129.26	13.351%	$146.5175	$146.52	$146.50	$146.50
Purchase #6	$67.94	6.378%	$72.2732	$72.27	$72.25	$72.30
Purchase #7	$217.82	12.378%	$244.7818	$244.78	$244.80	$244.80
7 purchase totals =	$870.13		$954.2506	$954.25	$954.25	$954.30