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	$232.49	6.192%	$246.8858	$246.89	$246.90	$246.90
Purchase #2	$248.77	7.657%	$267.8183	$267.82	$267.80	$267.80
Purchase #3	$87.91	3.213%	$90.7345	$90.73	$90.75	$90.70
Purchase #4	$109.45	8.570%	$118.8299	$118.83	$118.85	$118.80
Purchase #5	$98.81	13.434%	$112.0841	$112.08	$112.10	$112.10
Purchase #6	$226.68	7.468%	$243.6085	$243.61	$243.60	$243.60
Purchase #7	$176.78	8.349%	$191.5394	$191.54	$191.55	$191.50
7 purchase totals =	$1,180.89		$1,271.5005	$1,271.50	$1,271.55	$1,271.40