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	$226.32	12.199%	$253.9288	$253.93	$253.95	$253.90
Purchase #2	$242.28	10.620%	$268.0101	$268.01	$268.00	$268.00
Purchase #3	$81.27	8.785%	$88.4096	$88.41	$88.40	$88.40
Purchase #4	$96.73	3.641%	$100.2519	$100.25	$100.25	$100.30
Purchase #5	$34.93	7.862%	$37.6762	$37.68	$37.70	$37.70
Purchase #6	$15.60	9.824%	$17.1325	$17.13	$17.15	$17.10
Purchase #7	$89.33	12.545%	$100.5364	$100.54	$100.55	$100.50
7 purchase totals =	$786.46		$865.9455	$865.95	$866.00	$865.90