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	$97.26	3.740%	$100.8975	$100.90	$100.90	$100.90
Purchase #2	$71.89	8.170%	$77.7634	$77.76	$77.75	$77.80
Purchase #3	$133.84	10.224%	$147.5238	$147.52	$147.50	$147.50
Purchase #4	$163.55	12.823%	$184.522	$184.52	$184.50	$184.50
Purchase #5	$37.64	13.515%	$42.727	$42.73	$42.75	$42.70
Purchase #6	$107.51	7.301%	$115.3593	$115.36	$115.35	$115.40
Purchase #7	$140.31	4.571%	$146.7236	$146.72	$146.70	$146.70
7 purchase totals =	$752.00		$815.5166	$815.51	$815.45	$815.50