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	$84.77	6.261%	$90.0774	$90.08	$90.10	$90.10
Purchase #2	$56.33	5.573%	$59.4693	$59.47	$59.45	$59.50
Purchase #3	$14.40	5.405%	$15.1783	$15.18	$15.20	$15.20
Purchase #4	$76.56	6.757%	$81.7332	$81.73	$81.75	$81.70
Purchase #5	$222.62	4.536%	$232.718	$232.72	$232.70	$232.70
Purchase #6	$42.29	8.540%	$45.9016	$45.90	$45.90	$45.90
Purchase #7	$178.25	10.834%	$197.5616	$197.56	$197.55	$197.60
7 purchase totals =	$675.22		$722.6394	$722.64	$722.65	$722.70