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	$192.27	8.229%	$208.0919	$208.09	$208.10	$208.10
Purchase #2	$84.40	5.787%	$89.2842	$89.28	$89.30	$89.30
Purchase #3	$136.74	6.174%	$145.1823	$145.18	$145.20	$145.20
Purchase #4	$40.60	5.675%	$42.9041	$42.90	$42.90	$42.90
Purchase #5	$74.37	4.316%	$77.5798	$77.58	$77.60	$77.60
Purchase #6	$167.42	13.345%	$189.7622	$189.76	$189.75	$189.80
Purchase #7	$74.69	11.838%	$83.5318	$83.53	$83.55	$83.50
7 purchase totals =	$770.49		$836.3363	$836.32	$836.40	$836.40