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	$27.49	5.515%	$29.0061	$29.01	$29.00	$29.00
Purchase #2	$192.43	4.110%	$200.3389	$200.34	$200.35	$200.30
Purchase #3	$196.44	13.401%	$222.7649	$222.76	$222.75	$222.80
Purchase #4	$189.68	3.653%	$196.609	$196.61	$196.60	$196.60
Purchase #5	$36.89	13.649%	$41.9251	$41.93	$41.95	$41.90
Purchase #6	$151.44	6.850%	$161.8136	$161.81	$161.80	$161.80
Purchase #7	$67.89	13.158%	$76.823	$76.82	$76.80	$76.80
7 purchase totals =	$862.26		$929.2806	$929.28	$929.25	$929.20