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	$39.91	13.433%	$45.2711	$45.27	$45.25	$45.30
Purchase #2	$105.70	3.307%	$109.1955	$109.20	$109.20	$109.20
Purchase #3	$35.42	10.816%	$39.251	$39.25	$39.25	$39.30
Purchase #4	$84.45	6.617%	$90.0381	$90.04	$90.05	$90.00
Purchase #5	$29.73	5.490%	$31.3622	$31.36	$31.35	$31.40
Purchase #6	$94.29	10.572%	$104.2583	$104.26	$104.25	$104.30
Purchase #7	$55.57	8.809%	$60.4652	$60.47	$60.45	$60.50
7 purchase totals =	$445.07		$479.8414	$479.85	$479.80	$480.00