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	$166.73	10.704%	$184.5768	$184.58	$184.60	$184.60
Purchase #2	$142.46	4.572%	$148.9733	$148.97	$148.95	$149.00
Purchase #3	$38.80	8.685%	$42.1698	$42.17	$42.15	$42.20
Purchase #4	$215.78	3.215%	$222.7173	$222.72	$222.70	$222.70
Purchase #5	$76.43	5.465%	$80.6069	$80.61	$80.60	$80.60
Purchase #6	$10.28	10.676%	$11.3775	$11.38	$11.40	$11.40
Purchase #7	$156.83	6.732%	$167.3878	$167.39	$167.40	$167.40
7 purchase totals =	$807.31		$857.8094	$857.82	$857.80	$857.90