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	$45.56	6.664%	$48.5961	$48.60	$48.60	$48.60
Purchase #2	$150.42	10.152%	$165.6906	$165.69	$165.70	$165.70
Purchase #3	$39.41	8.677%	$42.8296	$42.83	$42.85	$42.80
Purchase #4	$214.29	5.855%	$226.8367	$226.84	$226.85	$226.80
Purchase #5	$53.88	10.355%	$59.4593	$59.46	$59.45	$59.50
Purchase #6	$82.62	5.696%	$87.326	$87.33	$87.35	$87.30
Purchase #7	$51.67	7.521%	$55.5561	$55.56	$55.55	$55.60
7 purchase totals =	$637.85		$686.2944	$686.31	$686.35	$686.30