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	$35.71	3.849%	$37.0845	$37.08	$37.10	$37.10
Purchase #2	$134.69	8.595%	$146.2666	$146.27	$146.25	$146.30
Purchase #3	$200.82	11.334%	$223.5809	$223.58	$223.60	$223.60
Purchase #4	$45.43	13.663%	$51.6371	$51.64	$51.65	$51.60
Purchase #5	$82.87	4.125%	$86.2884	$86.29	$86.30	$86.30
Purchase #6	$234.28	10.392%	$258.6264	$258.63	$258.65	$258.60
Purchase #7	$239.99	13.287%	$271.8775	$271.88	$271.90	$271.90
7 purchase totals =	$973.79		$1,075.3614	$1,075.37	$1,075.45	$1,075.40