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	$50.76	13.476%	$57.6004	$57.60	$57.60	$57.60
Purchase #2	$139.78	6.181%	$148.4198	$148.42	$148.40	$148.40
Purchase #3	$199.43	6.118%	$211.6311	$211.63	$211.65	$211.60
Purchase #4	$168.99	9.491%	$185.0288	$185.03	$185.05	$185.00
Purchase #5	$157.28	8.639%	$170.8674	$170.87	$170.85	$170.90
Purchase #6	$206.55	9.231%	$225.6166	$225.62	$225.60	$225.60
Purchase #7	$137.85	9.475%	$150.9113	$150.91	$150.90	$150.90
7 purchase totals =	$1,060.64		$1,150.0754	$1,150.08	$1,150.05	$1,150.00