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	$124.79	4.632%	$130.5703	$130.57	$130.55	$130.60
Purchase #2	$43.65	3.767%	$45.2943	$45.29	$45.30	$45.30
Purchase #3	$84.33	6.824%	$90.0847	$90.08	$90.10	$90.10
Purchase #4	$145.45	8.647%	$158.0271	$158.03	$158.05	$158.00
Purchase #5	$20.46	5.329%	$21.5503	$21.55	$21.55	$21.60
Purchase #6	$189.89	11.838%	$212.3692	$212.37	$212.35	$212.40
Purchase #7	$223.89	7.208%	$240.028	$240.03	$240.05	$240.00
7 purchase totals =	$832.46		$897.9239	$897.92	$897.95	$898.00