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	$227.30	3.202%	$234.5781	$234.58	$234.60	$234.60
Purchase #2	$108.52	9.180%	$118.4821	$118.48	$118.50	$118.50
Purchase #3	$113.45	10.390%	$125.2375	$125.24	$125.25	$125.20
Purchase #4	$141.96	3.501%	$146.93	$146.93	$146.95	$146.90
Purchase #5	$56.92	9.865%	$62.5352	$62.54	$62.55	$62.50
Purchase #6	$63.72	12.240%	$71.5193	$71.52	$71.50	$71.50
Purchase #7	$148.48	3.364%	$153.4749	$153.47	$153.45	$153.50
7 purchase totals =	$860.35		$912.7571	$912.76	$912.80	$912.70