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	$160.59	3.104%	$165.5747	$165.57	$165.55	$165.60
Purchase #2	$44.39	11.449%	$49.4722	$49.47	$49.45	$49.50
Purchase #3	$53.97	9.418%	$59.0529	$59.05	$59.05	$59.10
Purchase #4	$225.67	8.680%	$245.2582	$245.26	$245.25	$245.30
Purchase #5	$173.37	9.748%	$190.2701	$190.27	$190.25	$190.30
Purchase #6	$27.80	7.228%	$29.8094	$29.81	$29.80	$29.80
Purchase #7	$19.48	3.584%	$20.1782	$20.18	$20.20	$20.20
7 purchase totals =	$705.27		$759.6157	$759.61	$759.55	$759.80