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	$76.49	8.412%	$82.9243	$82.92	$82.90	$82.90
Purchase #2	$59.74	7.329%	$64.1183	$64.12	$64.10	$64.10
Purchase #3	$202.86	13.490%	$230.2258	$230.23	$230.25	$230.20
Purchase #4	$153.71	5.695%	$162.4638	$162.46	$162.45	$162.50
Purchase #5	$148.54	6.532%	$158.2426	$158.24	$158.25	$158.20
Purchase #6	$57.82	9.469%	$63.295	$63.30	$63.30	$63.30
Purchase #7	$95.89	7.592%	$103.17	$103.17	$103.15	$103.20
7 purchase totals =	$795.05		$864.4398	$864.44	$864.40	$864.40