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	$99.71	12.749%	$112.422	$112.42	$112.40	$112.40
Purchase #2	$139.42	4.642%	$145.8919	$145.89	$145.90	$145.90
Purchase #3	$175.32	4.586%	$183.3602	$183.36	$183.35	$183.40
Purchase #4	$74.85	5.265%	$78.7909	$78.79	$78.80	$78.80
Purchase #5	$98.68	4.408%	$103.0298	$103.03	$103.05	$103.00
Purchase #6	$50.58	6.826%	$54.0326	$54.03	$54.05	$54.00
Purchase #7	$184.46	10.137%	$203.1587	$203.16	$203.15	$203.20
7 purchase totals =	$823.02		$880.6861	$880.68	$880.70	$880.70