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	$72.72	12.413%	$81.7467	$81.75	$81.75	$81.70
Purchase #2	$35.65	12.307%	$40.0374	$40.04	$40.05	$40.00
Purchase #3	$250.72	5.509%	$264.5322	$264.53	$264.55	$264.50
Purchase #4	$22.92	3.768%	$23.7836	$23.78	$23.80	$23.80
Purchase #5	$177.33	6.229%	$188.3759	$188.38	$188.40	$188.40
Purchase #6	$108.85	13.499%	$123.5437	$123.54	$123.55	$123.50
Purchase #7	$177.36	8.746%	$192.8719	$192.87	$192.85	$192.90
7 purchase totals =	$845.55		$914.8914	$914.89	$914.95	$914.80