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	$30.77	13.377%	$34.8861	$34.89	$34.90	$34.90
Purchase #2	$58.97	4.436%	$61.5859	$61.59	$61.60	$61.60
Purchase #3	$117.36	3.769%	$121.7833	$121.78	$121.80	$121.80
Purchase #4	$151.35	5.291%	$159.3579	$159.36	$159.35	$159.40
Purchase #5	$78.48	5.515%	$82.8082	$82.81	$82.80	$82.80
Purchase #6	$190.84	8.321%	$206.7198	$206.72	$206.70	$206.70
Purchase #7	$90.77	10.260%	$100.083	$100.08	$100.10	$100.10
7 purchase totals =	$718.54		$767.2242	$767.23	$767.25	$767.30