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	$123.55	5.665%	$130.5491	$130.55	$130.55	$130.50
Purchase #2	$37.68	8.640%	$40.9356	$40.94	$40.95	$40.90
Purchase #3	$158.46	7.442%	$170.2526	$170.25	$170.25	$170.30
Purchase #4	$45.84	7.409%	$49.2363	$49.24	$49.25	$49.20
Purchase #5	$200.72	6.661%	$214.09	$214.09	$214.10	$214.10
Purchase #6	$173.55	10.415%	$191.6252	$191.63	$191.65	$191.60
Purchase #7	$120.71	13.383%	$136.8646	$136.86	$136.85	$136.90
7 purchase totals =	$860.51		$933.5534	$933.56	$933.60	$933.50