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	$69.25	4.578%	$72.4203	$72.42	$72.40	$72.40
Purchase #2	$204.80	5.793%	$216.6641	$216.66	$216.65	$216.70
Purchase #3	$25.27	10.370%	$27.8905	$27.89	$27.90	$27.90
Purchase #4	$60.60	3.293%	$62.5956	$62.60	$62.60	$62.60
Purchase #5	$133.75	3.127%	$137.9324	$137.93	$137.95	$137.90
Purchase #6	$84.81	7.266%	$90.9723	$90.97	$90.95	$91.00
Purchase #7	$66.49	7.146%	$71.2414	$71.24	$71.25	$71.20
7 purchase totals =	$644.97		$679.7166	$679.71	$679.70	$679.70