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	$138.90	9.693%	$152.3636	$152.36	$152.35	$152.40
Purchase #2	$171.52	11.104%	$190.5656	$190.57	$190.55	$190.60
Purchase #3	$11.73	4.139%	$12.2155	$12.22	$12.20	$12.20
Purchase #4	$160.55	4.244%	$167.3637	$167.36	$167.35	$167.40
Purchase #5	$213.43	11.758%	$238.5251	$238.53	$238.55	$238.50
Purchase #6	$100.97	10.388%	$111.4588	$111.46	$111.45	$111.50
Purchase #7	$56.38	9.341%	$61.6465	$61.65	$61.65	$61.60
7 purchase totals =	$853.48		$934.1388	$934.15	$934.10	$934.20