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	$17.87	3.871%	$18.5617	$18.56	$18.55	$18.60
Purchase #2	$187.71	13.196%	$212.4802	$212.48	$212.50	$212.50
Purchase #3	$30.69	9.363%	$33.5635	$33.56	$33.55	$33.60
Purchase #4	$122.47	12.495%	$137.7726	$137.77	$137.75	$137.80
Purchase #5	$109.30	13.211%	$123.7396	$123.74	$123.75	$123.70
Purchase #6	$50.97	6.371%	$54.2173	$54.22	$54.20	$54.20
Purchase #7	$23.37	9.387%	$25.5637	$25.56	$25.55	$25.60
7 purchase totals =	$542.38		$605.8986	$605.89	$605.85	$606.00