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	$228.41	11.867%	$255.5154	$255.52	$255.50	$255.50
Purchase #2	$10.29	4.808%	$10.7847	$10.78	$10.80	$10.80
Purchase #3	$42.37	10.758%	$46.9282	$46.93	$46.95	$46.90
Purchase #4	$24.59	11.726%	$27.4734	$27.47	$27.45	$27.50
Purchase #5	$54.81	4.681%	$57.3757	$57.38	$57.40	$57.40
Purchase #6	$49.53	11.760%	$55.3547	$55.35	$55.35	$55.40
Purchase #7	$189.51	9.373%	$207.2728	$207.27	$207.25	$207.30
7 purchase totals =	$599.51		$660.7049	$660.70	$660.70	$660.80