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	$95.76	4.732%	$100.2914	$100.29	$100.30	$100.30
Purchase #2	$71.28	10.785%	$78.9675	$78.97	$78.95	$79.00
Purchase #3	$166.94	5.359%	$175.8863	$175.89	$175.90	$175.90
Purchase #4	$94.58	10.305%	$104.3265	$104.33	$104.35	$104.30
Purchase #5	$109.63	8.171%	$118.5879	$118.59	$118.60	$118.60
Purchase #6	$131.25	7.381%	$140.9376	$140.94	$140.95	$140.90
Purchase #7	$88.65	12.452%	$99.6887	$99.69	$99.70	$99.70
7 purchase totals =	$758.09		$818.6859	$818.70	$818.75	$818.70