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	$151.86	10.839%	$168.3201	$168.32	$168.30	$168.30
Purchase #2	$98.58	7.330%	$105.8059	$105.81	$105.80	$105.80
Purchase #3	$11.64	12.794%	$13.1292	$13.13	$13.15	$13.10
Purchase #4	$30.76	10.207%	$33.8997	$33.90	$33.90	$33.90
Purchase #5	$10.58	10.317%	$11.6715	$11.67	$11.65	$11.70
Purchase #6	$63.34	5.639%	$66.9117	$66.91	$66.90	$66.90
Purchase #7	$223.53	8.194%	$241.846	$241.85	$241.85	$241.80
7 purchase totals =	$590.29		$641.5841	$641.59	$641.55	$641.50