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	$5.43	9.664%	$5.9548	$5.95	$5.95	$6.00
Purchase #2	$98.25	4.349%	$102.5229	$102.52	$102.50	$102.50
Purchase #3	$106.25	4.478%	$111.0079	$111.01	$111.00	$111.00
Purchase #4	$169.25	9.344%	$185.0647	$185.06	$185.05	$185.10
Purchase #5	$144.91	12.404%	$162.8846	$162.88	$162.90	$162.90
Purchase #6	$99.68	13.533%	$113.1697	$113.17	$113.15	$113.20
Purchase #7	$146.49	7.491%	$157.4636	$157.46	$157.45	$157.50
7 purchase totals =	$770.26		$838.0682	$838.05	$838.00	$838.20