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	$35.60	4.201%	$37.0956	$37.10	$37.10	$37.10
Purchase #2	$75.69	5.644%	$79.9619	$79.96	$79.95	$80.00
Purchase #3	$45.88	10.208%	$50.5634	$50.56	$50.55	$50.60
Purchase #4	$240.92	6.199%	$255.8546	$255.85	$255.85	$255.90
Purchase #5	$112.30	6.492%	$119.5905	$119.59	$119.60	$119.60
Purchase #6	$10.40	9.593%	$11.3977	$11.40	$11.40	$11.40
Purchase #7	$36.49	10.634%	$40.3703	$40.37	$40.35	$40.40
7 purchase totals =	$557.28		$594.8340	$594.83	$594.80	$595.00