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	$68.88	5.738%	$72.8323	$72.83	$72.85	$72.80
Purchase #2	$151.48	4.537%	$158.3526	$158.35	$158.35	$158.40
Purchase #3	$238.95	4.414%	$249.4973	$249.50	$249.50	$249.50
Purchase #4	$147.27	13.747%	$167.5152	$167.52	$167.50	$167.50
Purchase #5	$106.81	7.141%	$114.4373	$114.44	$114.45	$114.40
Purchase #6	$27.45	3.209%	$28.3309	$28.33	$28.35	$28.30
Purchase #7	$44.82	9.209%	$48.9475	$48.95	$48.95	$48.90
7 purchase totals =	$785.66		$839.9131	$839.92	$839.95	$839.80