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	$81.83	13.513%	$92.8877	$92.89	$92.90	$92.90
Purchase #2	$158.30	5.764%	$167.4244	$167.42	$167.40	$167.40
Purchase #3	$168.43	11.363%	$187.5687	$187.57	$187.55	$187.60
Purchase #4	$144.74	10.546%	$160.0043	$160.00	$160.00	$160.00
Purchase #5	$154.47	12.504%	$173.7849	$173.78	$173.80	$173.80
Purchase #6	$5.32	11.383%	$5.9256	$5.93	$5.95	$5.90
Purchase #7	$141.35	5.356%	$148.9207	$148.92	$148.90	$148.90
7 purchase totals =	$854.44		$936.5163	$936.51	$936.50	$936.50