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	$48.37	10.288%	$53.3463	$53.35	$53.35	$53.30
Purchase #2	$154.90	8.356%	$167.8434	$167.84	$167.85	$167.80
Purchase #3	$35.45	6.577%	$37.7815	$37.78	$37.80	$37.80
Purchase #4	$135.67	3.631%	$140.5962	$140.60	$140.60	$140.60
Purchase #5	$230.78	3.874%	$239.7204	$239.72	$239.70	$239.70
Purchase #6	$136.66	5.655%	$144.3881	$144.39	$144.40	$144.40
Purchase #7	$174.55	11.508%	$194.6372	$194.64	$194.65	$194.60
7 purchase totals =	$916.38		$978.3131	$978.32	$978.35	$978.20