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	$38.37	6.313%	$40.7923	$40.79	$40.80	$40.80
Purchase #2	$238.39	8.117%	$257.7401	$257.74	$257.75	$257.70
Purchase #3	$38.91	12.494%	$43.7714	$43.77	$43.75	$43.80
Purchase #4	$82.69	8.487%	$89.7079	$89.71	$89.70	$89.70
Purchase #5	$147.68	4.514%	$154.3463	$154.35	$154.35	$154.30
Purchase #6	$139.98	5.365%	$147.4899	$147.49	$147.50	$147.50
Purchase #7	$51.89	5.572%	$54.7813	$54.78	$54.80	$54.80
7 purchase totals =	$737.91		$788.6292	$788.63	$788.65	$788.60