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	$211.50	9.229%	$231.0193	$231.02	$231.00	$231.00
Purchase #2	$153.48	13.145%	$173.6549	$173.65	$173.65	$173.70
Purchase #3	$139.86	6.212%	$148.5481	$148.55	$148.55	$148.50
Purchase #4	$136.32	6.138%	$144.6873	$144.69	$144.70	$144.70
Purchase #5	$32.78	11.238%	$36.4638	$36.46	$36.45	$36.50
Purchase #6	$176.81	8.182%	$191.2766	$191.28	$191.30	$191.30
Purchase #7	$48.56	10.225%	$53.5253	$53.53	$53.55	$53.50
7 purchase totals =	$899.31		$979.1753	$979.18	$979.20	$979.20