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	$35.57	12.674%	$40.0781	$40.08	$40.10	$40.10
Purchase #2	$170.52	8.174%	$184.4583	$184.46	$184.45	$184.50
Purchase #3	$140.91	11.298%	$156.83	$156.83	$156.85	$156.80
Purchase #4	$167.27	8.802%	$181.9931	$181.99	$182.00	$182.00
Purchase #5	$140.55	11.190%	$156.2775	$156.28	$156.30	$156.30
Purchase #6	$10.82	8.639%	$11.7547	$11.75	$11.75	$11.80
Purchase #7	$102.40	8.542%	$111.147	$111.15	$111.15	$111.10
7 purchase totals =	$768.04		$842.5387	$842.54	$842.60	$842.60