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	$146.89	13.603%	$166.8714	$166.87	$166.85	$166.90
Purchase #2	$183.71	9.166%	$200.5489	$200.55	$200.55	$200.50
Purchase #3	$62.61	3.384%	$64.7287	$64.73	$64.75	$64.70
Purchase #4	$126.43	8.683%	$137.4079	$137.41	$137.40	$137.40
Purchase #5	$30.63	10.835%	$33.9488	$33.95	$33.95	$33.90
Purchase #6	$142.49	6.693%	$152.0269	$152.03	$152.05	$152.00
Purchase #7	$40.76	4.680%	$42.6676	$42.67	$42.65	$42.70
7 purchase totals =	$733.52		$798.2002	$798.21	$798.20	$798.10