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	$99.30	12.685%	$111.8962	$111.90	$111.90	$111.90
Purchase #2	$27.31	5.339%	$28.7681	$28.77	$28.75	$28.80
Purchase #3	$223.42	12.179%	$250.6303	$250.63	$250.65	$250.60
Purchase #4	$25.78	8.699%	$28.0226	$28.02	$28.00	$28.00
Purchase #5	$138.60	6.565%	$147.6991	$147.70	$147.70	$147.70
Purchase #6	$28.37	4.439%	$29.6293	$29.63	$29.65	$29.60
Purchase #7	$69.89	12.836%	$78.8611	$78.86	$78.85	$78.90
7 purchase totals =	$612.67		$675.5067	$675.51	$675.50	$675.50