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	$229.47	12.303%	$257.7017	$257.70	$257.70	$257.70
Purchase #2	$84.78	6.264%	$90.0906	$90.09	$90.10	$90.10
Purchase #3	$9.40	10.658%	$10.4019	$10.40	$10.40	$10.40
Purchase #4	$204.92	8.490%	$222.3177	$222.32	$222.30	$222.30
Purchase #5	$163.65	5.295%	$172.3153	$172.32	$172.30	$172.30
Purchase #6	$126.51	3.805%	$131.3237	$131.32	$131.30	$131.30
Purchase #7	$37.41	12.311%	$42.0155	$42.02	$42.00	$42.00
7 purchase totals =	$856.14		$926.1664	$926.17	$926.10	$926.10