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	$206.63	8.368%	$223.9208	$223.92	$223.90	$223.90
Purchase #2	$46.29	13.713%	$52.6377	$52.64	$52.65	$52.60
Purchase #3	$27.32	12.109%	$30.6282	$30.63	$30.65	$30.60
Purchase #4	$38.94	3.866%	$40.4454	$40.45	$40.45	$40.40
Purchase #5	$36.57	12.847%	$41.2681	$41.27	$41.25	$41.30
Purchase #6	$127.53	6.821%	$136.2288	$136.23	$136.25	$136.20
Purchase #7	$232.60	13.401%	$263.7707	$263.77	$263.75	$263.80
7 purchase totals =	$715.88		$788.8997	$788.91	$788.90	$788.80