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	$11.37	6.786%	$12.1416	$12.14	$12.15	$12.10
Purchase #2	$57.39	8.613%	$62.333	$62.33	$62.35	$62.30
Purchase #3	$192.99	6.282%	$205.1136	$205.11	$205.10	$205.10
Purchase #4	$39.60	6.140%	$42.0314	$42.03	$42.05	$42.00
Purchase #5	$37.79	12.721%	$42.5973	$42.60	$42.60	$42.60
Purchase #6	$160.45	6.162%	$170.3369	$170.34	$170.35	$170.30
Purchase #7	$179.63	9.573%	$196.826	$196.83	$196.85	$196.80
7 purchase totals =	$679.22		$731.3798	$731.38	$731.45	$731.20