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	$28.27	10.653%	$31.2816	$31.28	$31.30	$31.30
Purchase #2	$167.70	4.693%	$175.5702	$175.57	$175.55	$175.60
Purchase #3	$51.81	3.329%	$53.5348	$53.53	$53.55	$53.50
Purchase #4	$108.27	4.665%	$113.3208	$113.32	$113.30	$113.30
Purchase #5	$241.35	12.491%	$271.497	$271.50	$271.50	$271.50
Purchase #6	$232.67	9.665%	$255.1576	$255.16	$255.15	$255.20
Purchase #7	$136.98	10.511%	$151.378	$151.38	$151.40	$151.40
7 purchase totals =	$967.05		$1,051.7400	$1,051.74	$1,051.75	$1,051.80