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	$223.91	5.868%	$237.049	$237.05	$237.05	$237.00
Purchase #2	$128.88	10.832%	$142.8403	$142.84	$142.85	$142.80
Purchase #3	$114.54	11.631%	$127.8621	$127.86	$127.85	$127.90
Purchase #4	$70.29	13.498%	$79.7777	$79.78	$79.80	$79.80
Purchase #5	$52.77	8.137%	$57.0639	$57.06	$57.05	$57.10
Purchase #6	$191.77	3.534%	$198.5472	$198.55	$198.55	$198.50
Purchase #7	$134.38	6.243%	$142.7693	$142.77	$142.75	$142.80
7 purchase totals =	$916.54		$985.9095	$985.91	$985.90	$985.90