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	$172.43	6.377%	$183.4259	$183.43	$183.45	$183.40
Purchase #2	$67.51	7.772%	$72.7569	$72.76	$72.75	$72.80
Purchase #3	$132.60	3.799%	$137.6375	$137.64	$137.65	$137.60
Purchase #4	$49.31	11.106%	$54.7864	$54.79	$54.80	$54.80
Purchase #5	$223.36	4.483%	$233.3732	$233.37	$233.35	$233.40
Purchase #6	$9.62	10.753%	$10.6544	$10.65	$10.65	$10.70
Purchase #7	$82.27	4.367%	$85.8627	$85.86	$85.85	$85.90
7 purchase totals =	$737.10		$778.4970	$778.50	$778.50	$778.60