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	$14.51	6.232%	$15.4143	$15.41	$15.40	$15.40
Purchase #2	$146.67	3.151%	$151.2916	$151.29	$151.30	$151.30
Purchase #3	$158.92	5.755%	$168.0658	$168.07	$168.05	$168.10
Purchase #4	$95.39	4.241%	$99.4355	$99.44	$99.45	$99.40
Purchase #5	$110.41	12.759%	$124.4972	$124.50	$124.50	$124.50
Purchase #6	$18.65	4.859%	$19.5562	$19.56	$19.55	$19.60
Purchase #7	$14.57	6.309%	$15.4892	$15.49	$15.50	$15.50
7 purchase totals =	$559.12		$593.7498	$593.76	$593.75	$593.80