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	$46.89	6.464%	$49.921	$49.92	$49.90	$49.90
Purchase #2	$114.86	4.560%	$120.0976	$120.10	$120.10	$120.10
Purchase #3	$123.34	7.243%	$132.2735	$132.27	$132.25	$132.30
Purchase #4	$50.92	5.140%	$53.5373	$53.54	$53.55	$53.50
Purchase #5	$126.93	11.740%	$141.8316	$141.83	$141.85	$141.80
Purchase #6	$233.73	8.618%	$253.8729	$253.87	$253.85	$253.90
Purchase #7	$104.71	6.620%	$111.6418	$111.64	$111.65	$111.60
7 purchase totals =	$801.38		$863.1757	$863.17	$863.15	$863.10