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	$37.73	6.834%	$40.3085	$40.31	$40.30	$40.30
Purchase #2	$155.37	7.760%	$167.4267	$167.43	$167.45	$167.40
Purchase #3	$136.90	7.798%	$147.5755	$147.58	$147.60	$147.60
Purchase #4	$243.44	4.721%	$254.9328	$254.93	$254.95	$254.90
Purchase #5	$53.97	4.595%	$56.4499	$56.45	$56.45	$56.40
Purchase #6	$18.47	8.515%	$20.0427	$20.04	$20.05	$20.00
Purchase #7	$75.83	13.211%	$85.8479	$85.85	$85.85	$85.80
7 purchase totals =	$721.71		$772.5840	$772.59	$772.65	$772.40