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	$199.30	5.597%	$210.4548	$210.45	$210.45	$210.50
Purchase #2	$61.93	10.150%	$68.2159	$68.22	$68.20	$68.20
Purchase #3	$101.98	13.267%	$115.5097	$115.51	$115.50	$115.50
Purchase #4	$33.30	6.381%	$35.4249	$35.42	$35.40	$35.40
Purchase #5	$120.81	11.636%	$134.8675	$134.87	$134.85	$134.90
Purchase #6	$77.96	5.371%	$82.1472	$82.15	$82.15	$82.10
Purchase #7	$131.86	13.697%	$149.9209	$149.92	$149.90	$149.90
7 purchase totals =	$727.14		$796.5409	$796.54	$796.45	$796.50