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	$175.40	13.808%	$199.6192	$199.62	$199.60	$199.60
Purchase #2	$51.32	12.463%	$57.716	$57.72	$57.70	$57.70
Purchase #3	$16.50	13.574%	$18.7397	$18.74	$18.75	$18.70
Purchase #4	$48.43	12.694%	$54.5777	$54.58	$54.60	$54.60
Purchase #5	$72.87	7.300%	$78.1895	$78.19	$78.20	$78.20
Purchase #6	$188.47	3.802%	$195.6356	$195.64	$195.65	$195.60
Purchase #7	$65.43	10.505%	$72.3034	$72.30	$72.30	$72.30
7 purchase totals =	$618.42		$676.7811	$676.79	$676.80	$676.70