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	$16.25	12.724%	$18.3177	$18.32	$18.30	$18.30
Purchase #2	$81.88	4.567%	$85.6195	$85.62	$85.60	$85.60
Purchase #3	$36.55	3.466%	$37.8168	$37.82	$37.80	$37.80
Purchase #4	$221.77	3.230%	$228.9332	$228.93	$228.95	$228.90
Purchase #5	$157.43	3.425%	$162.822	$162.82	$162.80	$162.80
Purchase #6	$150.92	7.235%	$161.8391	$161.84	$161.85	$161.80
Purchase #7	$85.41	7.231%	$91.586	$91.59	$91.60	$91.60
7 purchase totals =	$750.21		$786.9343	$786.94	$786.90	$786.80