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	$11.85	3.368%	$12.2491	$12.25	$12.25	$12.20
Purchase #2	$129.61	10.215%	$142.8497	$142.85	$142.85	$142.80
Purchase #3	$152.59	4.107%	$158.8569	$158.86	$158.85	$158.90
Purchase #4	$124.28	6.150%	$131.9232	$131.92	$131.90	$131.90
Purchase #5	$92.40	5.314%	$97.3101	$97.31	$97.30	$97.30
Purchase #6	$83.54	13.444%	$94.7711	$94.77	$94.75	$94.80
Purchase #7	$179.61	11.343%	$199.9832	$199.98	$200.00	$200.00
7 purchase totals =	$773.88		$837.9433	$837.94	$837.90	$837.90