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	$130.70	6.862%	$139.6686	$139.67	$139.65	$139.70
Purchase #2	$72.55	11.325%	$80.7663	$80.77	$80.75	$80.80
Purchase #3	$38.78	11.309%	$43.1656	$43.17	$43.15	$43.20
Purchase #4	$9.69	10.359%	$10.6938	$10.69	$10.70	$10.70
Purchase #5	$102.86	8.792%	$111.9035	$111.90	$111.90	$111.90
Purchase #6	$141.26	4.788%	$148.0235	$148.02	$148.00	$148.00
Purchase #7	$90.27	6.313%	$95.9687	$95.97	$95.95	$96.00
7 purchase totals =	$586.11		$630.1900	$630.19	$630.10	$630.30