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	$49.80	9.410%	$54.4862	$54.49	$54.50	$54.50
Purchase #2	$145.71	13.822%	$165.85	$165.85	$165.85	$165.90
Purchase #3	$100.73	5.662%	$106.4333	$106.43	$106.45	$106.40
Purchase #4	$96.57	7.812%	$104.114	$104.11	$104.10	$104.10
Purchase #5	$128.72	13.325%	$145.8719	$145.87	$145.85	$145.90
Purchase #6	$186.34	7.191%	$199.7397	$199.74	$199.75	$199.70
Purchase #7	$168.83	9.655%	$185.1305	$185.13	$185.15	$185.10
7 purchase totals =	$876.70		$961.6256	$961.62	$961.65	$961.60