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	$36.69	3.381%	$37.9305	$37.93	$37.95	$37.90
Purchase #2	$246.60	11.193%	$274.2019	$274.20	$274.20	$274.20
Purchase #3	$9.64	12.637%	$10.8582	$10.86	$10.85	$10.90
Purchase #4	$106.36	8.712%	$115.6261	$115.63	$115.65	$115.60
Purchase #5	$45.49	4.439%	$47.5093	$47.51	$47.50	$47.50
Purchase #6	$115.62	3.312%	$119.4493	$119.45	$119.45	$119.40
Purchase #7	$54.53	13.376%	$61.8239	$61.82	$61.80	$61.80
7 purchase totals =	$614.93		$667.3992	$667.40	$667.40	$667.30