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	$52.38	3.142%	$54.0258	$54.03	$54.05	$54.00
Purchase #2	$42.86	9.360%	$46.8717	$46.87	$46.85	$46.90
Purchase #3	$10.91	10.404%	$12.0451	$12.05	$12.05	$12.00
Purchase #4	$21.46	13.320%	$24.3185	$24.32	$24.30	$24.30
Purchase #5	$26.34	5.300%	$27.736	$27.74	$27.75	$27.70
Purchase #6	$224.28	7.660%	$241.4598	$241.46	$241.45	$241.50
Purchase #7	$249.75	5.402%	$263.2415	$263.24	$263.25	$263.20
7 purchase totals =	$627.98		$669.6984	$669.71	$669.70	$669.60