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	$25.61	12.696%	$28.8614	$28.86	$28.85	$28.90
Purchase #2	$31.62	5.335%	$33.3069	$33.31	$33.30	$33.30
Purchase #3	$81.29	13.455%	$92.2276	$92.23	$92.25	$92.20
Purchase #4	$234.92	9.345%	$256.8733	$256.87	$256.85	$256.90
Purchase #5	$169.52	12.682%	$191.0185	$191.02	$191.00	$191.00
Purchase #6	$76.60	3.322%	$79.1447	$79.14	$79.15	$79.10
Purchase #7	$52.80	5.855%	$55.8914	$55.89	$55.90	$55.90
7 purchase totals =	$672.36		$737.3238	$737.32	$737.30	$737.30