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	$65.80	13.789%	$74.8732	$74.87	$74.85	$74.90
Purchase #2	$31.47	3.502%	$32.5721	$32.57	$32.55	$32.60
Purchase #3	$128.47	13.518%	$145.8366	$145.84	$145.85	$145.80
Purchase #4	$42.28	10.765%	$46.8314	$46.83	$46.85	$46.80
Purchase #5	$138.77	6.261%	$147.4584	$147.46	$147.45	$147.50
Purchase #6	$29.98	12.188%	$33.634	$33.63	$33.65	$33.60
Purchase #7	$42.69	7.574%	$45.9233	$45.92	$45.90	$45.90
7 purchase totals =	$479.46		$527.1290	$527.12	$527.10	$527.10