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	$150.56	13.505%	$170.8931	$170.89	$170.90	$170.90
Purchase #2	$223.57	8.857%	$243.3716	$243.37	$243.35	$243.40
Purchase #3	$228.71	12.251%	$256.7293	$256.73	$256.75	$256.70
Purchase #4	$159.56	4.677%	$167.0226	$167.02	$167.00	$167.00
Purchase #5	$190.55	7.330%	$204.5173	$204.52	$204.50	$204.50
Purchase #6	$137.27	7.361%	$147.3744	$147.37	$147.35	$147.40
Purchase #7	$79.61	13.849%	$90.6352	$90.64	$90.65	$90.60
7 purchase totals =	$1,169.83		$1,280.5435	$1,280.54	$1,280.50	$1,280.50