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	$99.52	12.737%	$112.1959	$112.20	$112.20	$112.20
Purchase #2	$165.81	3.375%	$171.4061	$171.41	$171.40	$171.40
Purchase #3	$158.50	12.679%	$178.5962	$178.60	$178.60	$178.60
Purchase #4	$33.83	10.765%	$37.4718	$37.47	$37.45	$37.50
Purchase #5	$192.98	4.717%	$202.0829	$202.08	$202.10	$202.10
Purchase #6	$99.50	10.128%	$109.5774	$109.58	$109.60	$109.60
Purchase #7	$27.70	13.460%	$31.4284	$31.43	$31.45	$31.40
7 purchase totals =	$777.84		$842.7587	$842.77	$842.80	$842.80