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	$94.38	6.783%	$100.7818	$100.78	$100.80	$100.80
Purchase #2	$19.86	6.618%	$21.1743	$21.17	$21.15	$21.20
Purchase #3	$149.46	12.544%	$168.2083	$168.21	$168.20	$168.20
Purchase #4	$180.57	6.657%	$192.5905	$192.59	$192.60	$192.60
Purchase #5	$48.94	4.760%	$51.2695	$51.27	$51.25	$51.30
Purchase #6	$59.37	11.865%	$66.4143	$66.41	$66.40	$66.40
Purchase #7	$118.41	8.705%	$128.7176	$128.72	$128.70	$128.70
7 purchase totals =	$670.99		$729.1563	$729.15	$729.10	$729.20