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	$18.29	10.664%	$20.2404	$20.24	$20.25	$20.20
Purchase #2	$248.61	6.445%	$264.6329	$264.63	$264.65	$264.60
Purchase #3	$227.47	11.485%	$253.5949	$253.59	$253.60	$253.60
Purchase #4	$34.47	3.326%	$35.6165	$35.62	$35.60	$35.60
Purchase #5	$233.60	8.641%	$253.7854	$253.79	$253.80	$253.80
Purchase #6	$82.60	9.821%	$90.7121	$90.71	$90.70	$90.70
Purchase #7	$16.98	9.527%	$18.5977	$18.60	$18.60	$18.60
7 purchase totals =	$862.02		$937.1799	$937.18	$937.20	$937.10