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	$215.61	12.224%	$241.9662	$241.97	$241.95	$242.00
Purchase #2	$133.66	13.323%	$151.4675	$151.47	$151.45	$151.50
Purchase #3	$46.90	3.404%	$48.4965	$48.50	$48.50	$48.50
Purchase #4	$139.46	8.559%	$151.3964	$151.40	$151.40	$151.40
Purchase #5	$71.35	9.773%	$78.323	$78.32	$78.30	$78.30
Purchase #6	$98.97	12.215%	$111.0592	$111.06	$111.05	$111.10
Purchase #7	$57.80	6.151%	$61.3553	$61.36	$61.35	$61.40
7 purchase totals =	$763.75		$844.0641	$844.08	$844.00	$844.20