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	$36.35	3.569%	$37.6473	$37.65	$37.65	$37.60
Purchase #2	$245.46	4.219%	$255.816	$255.82	$255.80	$255.80
Purchase #3	$111.76	3.162%	$115.2939	$115.29	$115.30	$115.30
Purchase #4	$179.66	9.394%	$196.5373	$196.54	$196.55	$196.50
Purchase #5	$134.39	8.233%	$145.4543	$145.45	$145.45	$145.50
Purchase #6	$64.66	7.220%	$69.3285	$69.33	$69.35	$69.30
Purchase #7	$66.76	6.247%	$70.9305	$70.93	$70.95	$70.90
7 purchase totals =	$839.04		$891.0078	$891.01	$891.05	$890.90