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	$149.35	11.779%	$166.9419	$166.94	$166.95	$166.90
Purchase #2	$52.33	6.640%	$55.8047	$55.80	$55.80	$55.80
Purchase #3	$137.70	10.674%	$152.3981	$152.40	$152.40	$152.40
Purchase #4	$132.90	7.226%	$142.5034	$142.50	$142.50	$142.50
Purchase #5	$57.98	12.200%	$65.0536	$65.05	$65.05	$65.10
Purchase #6	$100.77	11.380%	$112.2376	$112.24	$112.25	$112.20
Purchase #7	$58.97	10.465%	$65.1412	$65.14	$65.15	$65.10
7 purchase totals =	$690.00		$760.0805	$760.07	$760.10	$760.00