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	$112.30	6.866%	$120.0105	$120.01	$120.00	$120.00
Purchase #2	$230.42	3.422%	$238.305	$238.31	$238.30	$238.30
Purchase #3	$83.72	12.412%	$94.1113	$94.11	$94.10	$94.10
Purchase #4	$196.59	10.830%	$217.8807	$217.88	$217.90	$217.90
Purchase #5	$18.90	11.329%	$21.0412	$21.04	$21.05	$21.00
Purchase #6	$169.65	13.441%	$192.4527	$192.45	$192.45	$192.50
Purchase #7	$30.33	11.613%	$33.8522	$33.85	$33.85	$33.90
7 purchase totals =	$841.91		$917.6536	$917.65	$917.65	$917.70