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	$87.56	3.763%	$90.8549	$90.85	$90.85	$90.90
Purchase #2	$213.34	4.288%	$222.488	$222.49	$222.50	$222.50
Purchase #3	$72.45	7.749%	$78.0642	$78.06	$78.05	$78.10
Purchase #4	$160.39	3.344%	$165.7534	$165.75	$165.75	$165.80
Purchase #5	$34.81	9.847%	$38.2377	$38.24	$38.25	$38.20
Purchase #6	$96.72	4.304%	$100.8828	$100.88	$100.90	$100.90
Purchase #7	$150.43	6.344%	$159.9733	$159.97	$159.95	$160.00
7 purchase totals =	$815.70		$856.2543	$856.24	$856.25	$856.40