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	$44.76	11.419%	$49.8711	$49.87	$49.85	$49.90
Purchase #2	$178.55	8.258%	$193.2947	$193.29	$193.30	$193.30
Purchase #3	$238.27	3.859%	$247.4648	$247.46	$247.45	$247.50
Purchase #4	$222.81	10.597%	$246.4212	$246.42	$246.40	$246.40
Purchase #5	$56.39	5.141%	$59.289	$59.29	$59.30	$59.30
Purchase #6	$103.88	12.471%	$116.8349	$116.83	$116.85	$116.80
Purchase #7	$248.45	10.774%	$275.218	$275.22	$275.20	$275.20
7 purchase totals =	$1,093.11		$1,188.3937	$1,188.38	$1,188.35	$1,188.40