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	$10.41	10.782%	$11.5324	$11.53	$11.55	$11.50
Purchase #2	$136.46	7.375%	$146.5239	$146.52	$146.50	$146.50
Purchase #3	$54.28	3.346%	$56.0962	$56.10	$56.10	$56.10
Purchase #4	$239.54	12.104%	$268.5339	$268.53	$268.55	$268.50
Purchase #5	$125.79	4.551%	$131.5147	$131.51	$131.50	$131.50
Purchase #6	$17.95	9.469%	$19.6497	$19.65	$19.65	$19.60
Purchase #7	$134.87	10.210%	$148.6402	$148.64	$148.65	$148.60
7 purchase totals =	$719.30		$782.4910	$782.48	$782.50	$782.30