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	$72.77	11.128%	$80.8678	$80.87	$80.85	$80.90
Purchase #2	$143.86	9.808%	$157.9698	$157.97	$157.95	$158.00
Purchase #3	$203.63	5.663%	$215.1616	$215.16	$215.15	$215.20
Purchase #4	$131.52	12.307%	$147.7062	$147.71	$147.70	$147.70
Purchase #5	$201.93	8.213%	$218.5145	$218.51	$218.50	$218.50
Purchase #6	$151.66	10.471%	$167.5403	$167.54	$167.55	$167.50
Purchase #7	$144.90	7.163%	$155.2792	$155.28	$155.30	$155.30
7 purchase totals =	$1,050.27		$1,143.0394	$1,143.04	$1,143.00	$1,143.10