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	$69.67	11.261%	$77.5155	$77.52	$77.50	$77.50
Purchase #2	$106.90	12.603%	$120.3726	$120.37	$120.35	$120.40
Purchase #3	$89.78	11.565%	$100.1631	$100.16	$100.15	$100.20
Purchase #4	$47.94	7.640%	$51.6026	$51.60	$51.60	$51.60
Purchase #5	$70.87	10.167%	$78.0754	$78.08	$78.10	$78.10
Purchase #6	$54.36	12.532%	$61.1724	$61.17	$61.15	$61.20
Purchase #7	$245.59	13.691%	$279.2137	$279.21	$279.20	$279.20
7 purchase totals =	$685.11		$768.1153	$768.11	$768.05	$768.20