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	$125.80	10.764%	$139.3411	$139.34	$139.35	$139.30
Purchase #2	$233.68	9.383%	$255.6062	$255.61	$255.60	$255.60
Purchase #3	$104.67	6.147%	$111.1041	$111.10	$111.10	$111.10
Purchase #4	$205.97	8.106%	$222.6659	$222.67	$222.65	$222.70
Purchase #5	$37.85	5.426%	$39.9037	$39.90	$39.90	$39.90
Purchase #6	$8.75	4.290%	$9.1254	$9.13	$9.15	$9.10
Purchase #7	$46.54	12.375%	$52.2993	$52.30	$52.30	$52.30
7 purchase totals =	$763.26		$830.0457	$830.05	$830.05	$830.00