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	$108.81	13.717%	$123.7355	$123.74	$123.75	$123.70
Purchase #2	$238.48	13.249%	$270.0762	$270.08	$270.10	$270.10
Purchase #3	$91.98	13.230%	$104.149	$104.15	$104.15	$104.10
Purchase #4	$140.62	9.215%	$153.5781	$153.58	$153.60	$153.60
Purchase #5	$12.76	10.117%	$14.0509	$14.05	$14.05	$14.10
Purchase #6	$47.69	12.534%	$53.6675	$53.67	$53.65	$53.70
Purchase #7	$184.46	6.456%	$196.3687	$196.37	$196.35	$196.40
7 purchase totals =	$824.80		$915.6259	$915.64	$915.65	$915.70