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	$81.89	13.448%	$92.9026	$92.90	$92.90	$92.90
Purchase #2	$148.86	12.540%	$167.527	$167.53	$167.55	$167.50
Purchase #3	$45.83	5.774%	$48.4762	$48.48	$48.50	$48.50
Purchase #4	$24.44	12.569%	$27.5119	$27.51	$27.50	$27.50
Purchase #5	$62.83	12.186%	$70.4865	$70.49	$70.50	$70.50
Purchase #6	$143.32	12.671%	$161.4801	$161.48	$161.50	$161.50
Purchase #7	$105.65	10.701%	$116.9556	$116.96	$116.95	$117.00
7 purchase totals =	$612.82		$685.3399	$685.35	$685.40	$685.40