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	$73.57	7.232%	$78.8906	$78.89	$78.90	$78.90
Purchase #2	$118.87	13.443%	$134.8497	$134.85	$134.85	$134.80
Purchase #3	$175.91	8.371%	$190.6354	$190.64	$190.65	$190.60
Purchase #4	$111.26	13.756%	$126.5649	$126.56	$126.55	$126.60
Purchase #5	$99.81	3.874%	$103.6766	$103.68	$103.70	$103.70
Purchase #6	$10.28	6.294%	$10.927	$10.93	$10.95	$10.90
Purchase #7	$65.72	6.181%	$69.7822	$69.78	$69.80	$69.80
7 purchase totals =	$655.42		$715.3264	$715.33	$715.40	$715.30