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	$91.89	9.496%	$100.6159	$100.62	$100.60	$100.60
Purchase #2	$90.41	8.808%	$98.3733	$98.37	$98.35	$98.40
Purchase #3	$240.88	5.372%	$253.8201	$253.82	$253.80	$253.80
Purchase #4	$86.91	9.499%	$95.1656	$95.17	$95.15	$95.20
Purchase #5	$175.71	13.106%	$198.7386	$198.74	$198.75	$198.70
Purchase #6	$38.72	3.580%	$40.1062	$40.11	$40.10	$40.10
Purchase #7	$126.58	11.413%	$141.0266	$141.03	$141.05	$141.00
7 purchase totals =	$851.10		$927.8463	$927.86	$927.80	$927.80