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	$80.34	4.334%	$83.8219	$83.82	$83.80	$83.80
Purchase #2	$223.88	4.481%	$233.9121	$233.91	$233.90	$233.90
Purchase #3	$34.69	11.433%	$38.6561	$38.66	$38.65	$38.70
Purchase #4	$36.44	7.509%	$39.1763	$39.18	$39.20	$39.20
Purchase #5	$104.55	3.701%	$108.4194	$108.42	$108.40	$108.40
Purchase #6	$9.63	7.414%	$10.344	$10.34	$10.35	$10.30
Purchase #7	$59.86	12.287%	$67.215	$67.22	$67.20	$67.20
7 purchase totals =	$549.39		$581.5448	$581.55	$581.50	$581.50