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	$118.86	4.346%	$124.0257	$124.03	$124.05	$124.00
Purchase #2	$244.87	6.523%	$260.8429	$260.84	$260.85	$260.80
Purchase #3	$149.60	6.166%	$158.8243	$158.82	$158.80	$158.80
Purchase #4	$42.61	3.565%	$44.129	$44.13	$44.15	$44.10
Purchase #5	$72.46	9.452%	$79.3089	$79.31	$79.30	$79.30
Purchase #6	$81.41	10.328%	$89.818	$89.82	$89.80	$89.80
Purchase #7	$174.94	5.491%	$184.546	$184.55	$184.55	$184.50
7 purchase totals =	$884.75		$941.4948	$941.50	$941.50	$941.30