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	$90.46	8.129%	$97.8135	$97.81	$97.80	$97.80
Purchase #2	$84.60	10.500%	$93.483	$93.48	$93.50	$93.50
Purchase #3	$78.47	13.764%	$89.2706	$89.27	$89.25	$89.30
Purchase #4	$127.96	8.202%	$138.4553	$138.46	$138.45	$138.50
Purchase #5	$100.40	5.380%	$105.8015	$105.80	$105.80	$105.80
Purchase #6	$131.56	11.639%	$146.8723	$146.87	$146.85	$146.90
Purchase #7	$234.98	13.397%	$266.4603	$266.46	$266.45	$266.50
7 purchase totals =	$848.43		$938.1565	$938.15	$938.10	$938.30