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	$87.27	9.750%	$95.7788	$95.78	$95.80	$95.80
Purchase #2	$97.51	3.347%	$100.7737	$100.77	$100.75	$100.80
Purchase #3	$143.55	13.270%	$162.5991	$162.60	$162.60	$162.60
Purchase #4	$63.75	3.867%	$66.2152	$66.22	$66.20	$66.20
Purchase #5	$155.75	9.531%	$170.5945	$170.59	$170.60	$170.60
Purchase #6	$99.79	11.342%	$111.1082	$111.11	$111.10	$111.10
Purchase #7	$130.77	12.713%	$147.3948	$147.39	$147.40	$147.40
7 purchase totals =	$778.39		$854.4643	$854.46	$854.45	$854.50