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	$65.66	11.429%	$73.1643	$73.16	$73.15	$73.20
Purchase #2	$159.27	11.615%	$177.7692	$177.77	$177.75	$177.80
Purchase #3	$241.50	12.766%	$272.3299	$272.33	$272.35	$272.30
Purchase #4	$38.30	9.611%	$41.981	$41.98	$42.00	$42.00
Purchase #5	$145.79	11.513%	$162.5748	$162.57	$162.55	$162.60
Purchase #6	$90.26	11.696%	$100.8168	$100.82	$100.80	$100.80
Purchase #7	$105.99	3.511%	$109.7113	$109.71	$109.70	$109.70
7 purchase totals =	$846.77		$938.3473	$938.34	$938.30	$938.40