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	$96.43	3.181%	$99.4974	$99.50	$99.50	$99.50
Purchase #2	$225.49	3.500%	$233.3822	$233.38	$233.40	$233.40
Purchase #3	$90.73	6.707%	$96.8153	$96.82	$96.80	$96.80
Purchase #4	$40.63	13.565%	$46.1415	$46.14	$46.15	$46.10
Purchase #5	$203.69	5.171%	$214.2228	$214.22	$214.20	$214.20
Purchase #6	$67.44	6.766%	$72.003	$72.00	$72.00	$72.00
Purchase #7	$110.82	8.359%	$120.0834	$120.08	$120.10	$120.10
7 purchase totals =	$835.23		$882.1456	$882.14	$882.15	$882.10