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	$243.93	5.540%	$257.4437	$257.44	$257.45	$257.40
Purchase #2	$151.89	5.551%	$160.3214	$160.32	$160.30	$160.30
Purchase #3	$226.54	4.748%	$237.2961	$237.30	$237.30	$237.30
Purchase #4	$130.57	9.198%	$142.5798	$142.58	$142.60	$142.60
Purchase #5	$37.60	3.439%	$38.8931	$38.89	$38.90	$38.90
Purchase #6	$50.37	12.352%	$56.5917	$56.59	$56.60	$56.60
Purchase #7	$30.40	11.660%	$33.9446	$33.94	$33.95	$33.90
7 purchase totals =	$871.30		$927.0704	$927.06	$927.10	$927.00