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	$8.56	6.198%	$9.0905	$9.09	$9.10	$9.10
Purchase #2	$82.97	11.147%	$92.2187	$92.22	$92.20	$92.20
Purchase #3	$72.81	10.669%	$80.5781	$80.58	$80.60	$80.60
Purchase #4	$189.36	3.781%	$196.5197	$196.52	$196.50	$196.50
Purchase #5	$16.79	4.609%	$17.5639	$17.56	$17.55	$17.60
Purchase #6	$37.68	7.157%	$40.3768	$40.38	$40.40	$40.40
Purchase #7	$44.68	6.240%	$47.468	$47.47	$47.45	$47.50
7 purchase totals =	$452.85		$483.8157	$483.82	$483.80	$483.90