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	$33.95	10.381%	$37.4743	$37.47	$37.45	$37.50
Purchase #2	$20.63	11.556%	$23.014	$23.01	$23.00	$23.00
Purchase #3	$107.83	7.458%	$115.872	$115.87	$115.85	$115.90
Purchase #4	$98.34	10.757%	$108.9184	$108.92	$108.90	$108.90
Purchase #5	$130.89	4.725%	$137.0746	$137.07	$137.05	$137.10
Purchase #6	$156.35	11.489%	$174.3131	$174.31	$174.30	$174.30
Purchase #7	$60.72	11.603%	$67.7653	$67.77	$67.75	$67.80
7 purchase totals =	$608.71		$664.4317	$664.42	$664.30	$664.50