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	$140.30	12.783%	$158.2345	$158.23	$158.25	$158.20
Purchase #2	$156.72	10.204%	$172.7117	$172.71	$172.70	$172.70
Purchase #3	$101.79	10.711%	$112.6927	$112.69	$112.70	$112.70
Purchase #4	$36.73	10.745%	$40.6766	$40.68	$40.70	$40.70
Purchase #5	$57.84	3.259%	$59.725	$59.73	$59.75	$59.70
Purchase #6	$162.73	4.664%	$170.3197	$170.32	$170.30	$170.30
Purchase #7	$116.88	12.829%	$131.8745	$131.87	$131.85	$131.90
7 purchase totals =	$772.99		$846.2347	$846.23	$846.25	$846.20