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	$27.82	9.127%	$30.3591	$30.36	$30.35	$30.40
Purchase #2	$113.85	5.637%	$120.2677	$120.27	$120.25	$120.30
Purchase #3	$215.81	4.146%	$224.7575	$224.76	$224.75	$224.80
Purchase #4	$168.26	11.360%	$187.3743	$187.37	$187.35	$187.40
Purchase #5	$49.64	11.584%	$55.3903	$55.39	$55.40	$55.40
Purchase #6	$188.91	6.130%	$200.4902	$200.49	$200.50	$200.50
Purchase #7	$91.43	10.376%	$100.9168	$100.92	$100.90	$100.90
7 purchase totals =	$855.72		$919.5559	$919.56	$919.50	$919.70