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	$123.82	6.528%	$131.903	$131.90	$131.90	$131.90
Purchase #2	$138.29	7.509%	$148.6742	$148.67	$148.65	$148.70
Purchase #3	$166.55	4.149%	$173.4602	$173.46	$173.45	$173.50
Purchase #4	$247.58	10.314%	$273.1154	$273.12	$273.10	$273.10
Purchase #5	$197.29	10.860%	$218.7157	$218.72	$218.70	$218.70
Purchase #6	$171.40	8.419%	$185.8302	$185.83	$185.85	$185.80
Purchase #7	$47.33	3.654%	$49.0594	$49.06	$49.05	$49.10
7 purchase totals =	$1,092.26		$1,180.7581	$1,180.76	$1,180.70	$1,180.80