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	$30.57	5.328%	$32.1988	$32.20	$32.20	$32.20
Purchase #2	$77.72	6.590%	$82.8417	$82.84	$82.85	$82.80
Purchase #3	$179.59	10.690%	$198.7882	$198.79	$198.80	$198.80
Purchase #4	$122.56	4.389%	$127.9392	$127.94	$127.95	$127.90
Purchase #5	$218.97	4.648%	$229.1477	$229.15	$229.15	$229.10
Purchase #6	$32.70	11.244%	$36.3768	$36.38	$36.40	$36.40
Purchase #7	$248.39	9.737%	$272.5757	$272.58	$272.60	$272.60
7 purchase totals =	$910.50		$979.8681	$979.88	$979.95	$979.80