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	$234.84	5.700%	$248.2259	$248.23	$248.25	$248.20
Purchase #2	$78.61	6.633%	$83.8242	$83.82	$83.80	$83.80
Purchase #3	$41.29	13.153%	$46.7209	$46.72	$46.70	$46.70
Purchase #4	$123.61	3.420%	$127.8375	$127.84	$127.85	$127.80
Purchase #5	$140.52	4.307%	$146.5722	$146.57	$146.55	$146.60
Purchase #6	$82.44	4.580%	$86.2158	$86.22	$86.20	$86.20
Purchase #7	$209.74	5.156%	$220.5542	$220.55	$220.55	$220.60
7 purchase totals =	$911.05		$959.9507	$959.95	$959.90	$959.90