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	$72.29	8.599%	$78.5062	$78.51	$78.50	$78.50
Purchase #2	$19.59	8.723%	$21.2988	$21.30	$21.30	$21.30
Purchase #3	$94.78	13.332%	$107.4161	$107.42	$107.40	$107.40
Purchase #4	$78.29	5.722%	$82.7698	$82.77	$82.75	$82.80
Purchase #5	$228.92	3.345%	$236.5774	$236.58	$236.60	$236.60
Purchase #6	$158.81	6.481%	$169.1025	$169.10	$169.10	$169.10
Purchase #7	$119.33	5.541%	$125.9421	$125.94	$125.95	$125.90
7 purchase totals =	$772.01		$821.6129	$821.62	$821.60	$821.60