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	$162.27	5.625%	$171.3977	$171.40	$171.40	$171.40
Purchase #2	$34.97	7.199%	$37.4875	$37.49	$37.50	$37.50
Purchase #3	$220.60	8.118%	$238.5083	$238.51	$238.50	$238.50
Purchase #4	$20.45	13.298%	$23.1694	$23.17	$23.15	$23.20
Purchase #5	$35.29	11.521%	$39.3558	$39.36	$39.35	$39.40
Purchase #6	$38.74	9.381%	$42.3742	$42.37	$42.35	$42.40
Purchase #7	$217.47	12.840%	$245.3931	$245.39	$245.40	$245.40
7 purchase totals =	$729.79		$797.6860	$797.69	$797.65	$797.80