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	$223.76	8.166%	$242.0322	$242.03	$242.05	$242.00
Purchase #2	$152.52	4.869%	$159.9462	$159.95	$159.95	$159.90
Purchase #3	$123.96	10.115%	$136.4986	$136.50	$136.50	$136.50
Purchase #4	$20.40	13.578%	$23.1699	$23.17	$23.15	$23.20
Purchase #5	$115.97	13.331%	$131.43	$131.43	$131.45	$131.40
Purchase #6	$18.89	13.302%	$21.4027	$21.40	$21.40	$21.40
Purchase #7	$120.27	10.144%	$132.4702	$132.47	$132.45	$132.50
7 purchase totals =	$775.77		$846.9498	$846.95	$846.95	$846.90