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	$134.75	8.821%	$146.6363	$146.64	$146.65	$146.60
Purchase #2	$99.82	5.692%	$105.5018	$105.50	$105.50	$105.50
Purchase #3	$211.62	7.673%	$227.8576	$227.86	$227.85	$227.90
Purchase #4	$54.58	7.549%	$58.7002	$58.70	$58.70	$58.70
Purchase #5	$98.68	5.591%	$104.1972	$104.20	$104.20	$104.20
Purchase #6	$85.90	4.272%	$89.5696	$89.57	$89.55	$89.60
Purchase #7	$235.25	11.510%	$262.3273	$262.33	$262.35	$262.30
7 purchase totals =	$920.60		$994.7900	$994.80	$994.80	$994.80