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	$86.34	6.360%	$91.8312	$91.83	$91.85	$91.80
Purchase #2	$111.43	7.536%	$119.8274	$119.83	$119.85	$119.80
Purchase #3	$68.51	13.275%	$77.6047	$77.60	$77.60	$77.60
Purchase #4	$34.30	9.571%	$37.5829	$37.58	$37.60	$37.60
Purchase #5	$104.61	3.570%	$108.3446	$108.34	$108.35	$108.30
Purchase #6	$149.29	12.499%	$167.9498	$167.95	$167.95	$167.90
Purchase #7	$199.60	13.378%	$226.3025	$226.30	$226.30	$226.30
7 purchase totals =	$754.08		$829.4431	$829.43	$829.50	$829.30