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	$37.83	8.243%	$40.9483	$40.95	$40.95	$40.90
Purchase #2	$87.26	13.276%	$98.8446	$98.84	$98.85	$98.80
Purchase #3	$48.75	9.282%	$53.275	$53.28	$53.30	$53.30
Purchase #4	$155.72	6.782%	$166.2809	$166.28	$166.30	$166.30
Purchase #5	$210.51	7.856%	$227.0477	$227.05	$227.05	$227.00
Purchase #6	$29.51	7.869%	$31.8321	$31.83	$31.85	$31.80
Purchase #7	$229.27	5.479%	$241.8317	$241.83	$241.85	$241.80
7 purchase totals =	$798.85		$860.0603	$860.06	$860.15	$859.90