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	$135.62	5.285%	$142.7875	$142.79	$142.80	$142.80
Purchase #2	$249.88	10.722%	$276.6721	$276.67	$276.65	$276.70
Purchase #3	$92.81	12.108%	$104.0474	$104.05	$104.05	$104.00
Purchase #4	$123.54	3.547%	$127.922	$127.92	$127.90	$127.90
Purchase #5	$94.46	4.612%	$98.8165	$98.82	$98.80	$98.80
Purchase #6	$59.30	10.197%	$65.3468	$65.35	$65.35	$65.30
Purchase #7	$46.54	12.792%	$52.4934	$52.49	$52.50	$52.50
7 purchase totals =	$802.15		$868.0857	$868.09	$868.05	$868.00