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	$97.50	3.247%	$100.6658	$100.67	$100.65	$100.70
Purchase #2	$97.94	5.276%	$103.1073	$103.11	$103.10	$103.10
Purchase #3	$90.91	11.554%	$101.4137	$101.41	$101.40	$101.40
Purchase #4	$173.42	9.633%	$190.1255	$190.13	$190.15	$190.10
Purchase #5	$77.92	10.826%	$86.3556	$86.36	$86.35	$86.40
Purchase #6	$95.43	4.479%	$99.7043	$99.70	$99.70	$99.70
Purchase #7	$156.26	5.121%	$164.2621	$164.26	$164.25	$164.30
7 purchase totals =	$789.38		$845.6343	$845.64	$845.60	$845.70