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	$33.41	12.368%	$37.5421	$37.54	$37.55	$37.50
Purchase #2	$45.52	12.600%	$51.2555	$51.26	$51.25	$51.30
Purchase #3	$196.91	3.803%	$204.3985	$204.40	$204.40	$204.40
Purchase #4	$37.81	8.471%	$41.0129	$41.01	$41.00	$41.00
Purchase #5	$49.63	9.720%	$54.454	$54.45	$54.45	$54.50
Purchase #6	$243.38	3.302%	$251.4164	$251.42	$251.40	$251.40
Purchase #7	$125.54	12.791%	$141.5978	$141.60	$141.60	$141.60
7 purchase totals =	$732.20		$781.6772	$781.68	$781.65	$781.70