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	$46.40	9.756%	$50.9268	$50.93	$50.95	$50.90
Purchase #2	$135.28	4.753%	$141.7099	$141.71	$141.70	$141.70
Purchase #3	$91.67	8.306%	$99.2841	$99.28	$99.30	$99.30
Purchase #4	$81.52	11.332%	$90.7578	$90.76	$90.75	$90.80
Purchase #5	$107.66	6.858%	$115.0433	$115.04	$115.05	$115.00
Purchase #6	$43.77	4.262%	$45.6355	$45.64	$45.65	$45.60
Purchase #7	$39.25	13.415%	$44.5154	$44.52	$44.50	$44.50
7 purchase totals =	$545.55		$587.8728	$587.88	$587.90	$587.80