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	$207.28	10.222%	$228.4682	$228.47	$228.45	$228.50
Purchase #2	$123.68	8.723%	$134.4686	$134.47	$134.45	$134.50
Purchase #3	$88.49	13.627%	$100.5485	$100.55	$100.55	$100.50
Purchase #4	$73.90	11.638%	$82.5005	$82.50	$82.50	$82.50
Purchase #5	$174.60	9.629%	$191.4122	$191.41	$191.40	$191.40
Purchase #6	$24.89	13.219%	$28.1802	$28.18	$28.20	$28.20
Purchase #7	$202.64	3.805%	$210.3505	$210.35	$210.35	$210.40
7 purchase totals =	$895.48		$975.9287	$975.93	$975.90	$976.00