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	$39.35	9.683%	$43.1603	$43.16	$43.15	$43.20
Purchase #2	$100.46	5.786%	$106.2726	$106.27	$106.25	$106.30
Purchase #3	$95.36	10.160%	$105.0486	$105.05	$105.05	$105.00
Purchase #4	$7.50	10.123%	$8.2592	$8.26	$8.25	$8.30
Purchase #5	$86.65	13.455%	$98.3088	$98.31	$98.30	$98.30
Purchase #6	$134.65	11.755%	$150.4781	$150.48	$150.50	$150.50
Purchase #7	$65.92	11.117%	$73.2483	$73.25	$73.25	$73.20
7 purchase totals =	$529.89		$584.7759	$584.78	$584.75	$584.80