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	$231.92	3.783%	$240.6935	$240.69	$240.70	$240.70
Purchase #2	$131.28	6.522%	$139.8421	$139.84	$139.85	$139.80
Purchase #3	$37.83	5.266%	$39.8221	$39.82	$39.80	$39.80
Purchase #4	$59.73	3.355%	$61.7339	$61.73	$61.75	$61.70
Purchase #5	$139.63	5.257%	$146.9703	$146.97	$146.95	$147.00
Purchase #6	$38.65	4.315%	$40.3177	$40.32	$40.30	$40.30
Purchase #7	$131.84	7.390%	$141.583	$141.58	$141.60	$141.60
7 purchase totals =	$770.88		$810.9626	$810.95	$810.95	$810.90