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	$89.65	10.667%	$99.213	$99.21	$99.20	$99.20
Purchase #2	$89.92	7.129%	$96.3304	$96.33	$96.35	$96.30
Purchase #3	$99.96	5.738%	$105.6957	$105.70	$105.70	$105.70
Purchase #4	$47.75	12.222%	$53.586	$53.59	$53.60	$53.60
Purchase #5	$203.59	9.289%	$222.5015	$222.50	$222.50	$222.50
Purchase #6	$231.85	12.110%	$259.927	$259.93	$259.95	$259.90
Purchase #7	$141.45	8.597%	$153.6105	$153.61	$153.60	$153.60
7 purchase totals =	$904.17		$990.8641	$990.87	$990.90	$990.80