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	$65.46	10.362%	$72.243	$72.24	$72.25	$72.20
Purchase #2	$155.65	12.474%	$175.0658	$175.07	$175.05	$175.10
Purchase #3	$45.34	5.629%	$47.8922	$47.89	$47.90	$47.90
Purchase #4	$6.81	11.538%	$7.5957	$7.60	$7.60	$7.60
Purchase #5	$52.43	7.350%	$56.2836	$56.28	$56.30	$56.30
Purchase #6	$116.71	13.861%	$132.8872	$132.89	$132.90	$132.90
Purchase #7	$38.71	8.250%	$41.9036	$41.90	$41.90	$41.90
7 purchase totals =	$481.11		$533.8711	$533.87	$533.90	$533.90