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	$45.52	13.689%	$51.7512	$51.75	$51.75	$51.80
Purchase #2	$147.69	13.497%	$167.6237	$167.62	$167.60	$167.60
Purchase #3	$52.68	12.318%	$59.1691	$59.17	$59.15	$59.20
Purchase #4	$17.59	12.451%	$19.7801	$19.78	$19.80	$19.80
Purchase #5	$206.98	13.409%	$234.7339	$234.73	$234.75	$234.70
Purchase #6	$80.59	11.409%	$89.7845	$89.78	$89.80	$89.80
Purchase #7	$57.75	6.853%	$61.7076	$61.71	$61.70	$61.70
7 purchase totals =	$608.80		$684.5501	$684.54	$684.55	$684.60