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	$149.59	3.869%	$155.3776	$155.38	$155.40	$155.40
Purchase #2	$41.44	10.550%	$45.8119	$45.81	$45.80	$45.80
Purchase #3	$117.52	3.351%	$121.4581	$121.46	$121.45	$121.50
Purchase #4	$243.89	5.289%	$256.7893	$256.79	$256.80	$256.80
Purchase #5	$87.54	7.831%	$94.3953	$94.40	$94.40	$94.40
Purchase #6	$80.32	11.596%	$89.6339	$89.63	$89.65	$89.60
Purchase #7	$52.34	8.121%	$56.5905	$56.59	$56.60	$56.60
7 purchase totals =	$772.64		$820.0566	$820.06	$820.10	$820.10