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	$180.30	6.131%	$191.3542	$191.35	$191.35	$191.40
Purchase #2	$19.46	8.870%	$21.1861	$21.19	$21.20	$21.20
Purchase #3	$27.36	6.776%	$29.2139	$29.21	$29.20	$29.20
Purchase #4	$25.76	7.610%	$27.7203	$27.72	$27.70	$27.70
Purchase #5	$85.67	5.230%	$90.1505	$90.15	$90.15	$90.20
Purchase #6	$186.43	4.238%	$194.3309	$194.33	$194.35	$194.30
Purchase #7	$78.61	9.406%	$86.0041	$86.00	$86.00	$86.00
7 purchase totals =	$603.59		$639.9600	$639.95	$639.95	$640.00