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	$14.54	9.834%	$15.9699	$15.97	$15.95	$16.00
Purchase #2	$36.68	4.475%	$38.3214	$38.32	$38.30	$38.30
Purchase #3	$44.59	12.628%	$50.2208	$50.22	$50.20	$50.20
Purchase #4	$89.40	6.532%	$95.2396	$95.24	$95.25	$95.20
Purchase #5	$55.46	7.530%	$59.6361	$59.64	$59.65	$59.60
Purchase #6	$36.41	11.413%	$40.5655	$40.57	$40.55	$40.60
Purchase #7	$143.58	7.254%	$153.9953	$154.00	$154.00	$154.00
7 purchase totals =	$420.66		$453.9486	$453.96	$453.90	$453.90