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	$35.86	10.596%	$39.6597	$39.66	$39.65	$39.70
Purchase #2	$106.83	10.388%	$117.9275	$117.93	$117.95	$117.90
Purchase #3	$48.30	8.763%	$52.5325	$52.53	$52.55	$52.50
Purchase #4	$127.30	11.200%	$141.5576	$141.56	$141.55	$141.60
Purchase #5	$167.54	8.109%	$181.1258	$181.13	$181.15	$181.10
Purchase #6	$82.60	10.311%	$91.1169	$91.12	$91.10	$91.10
Purchase #7	$174.42	12.718%	$196.6027	$196.60	$196.60	$196.60
7 purchase totals =	$742.85		$820.5227	$820.53	$820.55	$820.50