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	$122.26	12.585%	$137.6464	$137.65	$137.65	$137.60
Purchase #2	$40.55	13.104%	$45.8637	$45.86	$45.85	$45.90
Purchase #3	$90.51	9.361%	$98.9826	$98.98	$99.00	$99.00
Purchase #4	$20.99	3.539%	$21.7328	$21.73	$21.75	$21.70
Purchase #5	$191.45	13.137%	$216.6008	$216.60	$216.60	$216.60
Purchase #6	$164.64	12.874%	$185.8358	$185.84	$185.85	$185.80
Purchase #7	$158.30	8.401%	$171.5988	$171.60	$171.60	$171.60
7 purchase totals =	$788.70		$878.2609	$878.26	$878.30	$878.20