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	$44.43	11.215%	$49.4128	$49.41	$49.40	$49.40
Purchase #2	$84.87	9.337%	$92.7943	$92.79	$92.80	$92.80
Purchase #3	$79.99	6.349%	$85.0686	$85.07	$85.05	$85.10
Purchase #4	$200.76	9.229%	$219.2881	$219.29	$219.30	$219.30
Purchase #5	$92.76	11.523%	$103.4487	$103.45	$103.45	$103.40
Purchase #6	$11.59	10.672%	$12.8269	$12.83	$12.85	$12.80
Purchase #7	$175.36	12.297%	$196.924	$196.92	$196.90	$196.90
7 purchase totals =	$689.76		$759.7634	$759.76	$759.75	$759.70