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	$34.80	10.478%	$38.4463	$38.45	$38.45	$38.40
Purchase #2	$202.75	9.616%	$222.2464	$222.25	$222.25	$222.20
Purchase #3	$138.55	5.459%	$146.1134	$146.11	$146.10	$146.10
Purchase #4	$25.31	12.328%	$28.4302	$28.43	$28.45	$28.40
Purchase #5	$56.68	8.516%	$61.5069	$61.51	$61.50	$61.50
Purchase #6	$155.28	12.371%	$174.4897	$174.49	$174.50	$174.50
Purchase #7	$32.95	11.167%	$36.6295	$36.63	$36.65	$36.60
7 purchase totals =	$646.32		$707.8624	$707.87	$707.90	$707.70