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	$155.57	9.802%	$170.819	$170.82	$170.80	$170.80
Purchase #2	$249.72	3.359%	$258.1081	$258.11	$258.10	$258.10
Purchase #3	$5.82	8.562%	$6.3183	$6.32	$6.30	$6.30
Purchase #4	$100.49	11.479%	$112.0252	$112.03	$112.05	$112.00
Purchase #5	$238.60	10.778%	$264.3163	$264.32	$264.30	$264.30
Purchase #6	$120.82	5.559%	$127.5364	$127.54	$127.55	$127.50
Purchase #7	$21.28	11.635%	$23.7559	$23.76	$23.75	$23.80
7 purchase totals =	$892.30		$962.8792	$962.90	$962.85	$962.80