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	$97.69	10.820%	$108.2601	$108.26	$108.25	$108.30
Purchase #2	$164.72	12.545%	$185.3841	$185.38	$185.40	$185.40
Purchase #3	$134.55	10.183%	$148.2512	$148.25	$148.25	$148.30
Purchase #4	$35.60	3.515%	$36.8513	$36.85	$36.85	$36.90
Purchase #5	$204.92	8.734%	$222.8177	$222.82	$222.80	$222.80
Purchase #6	$166.25	6.817%	$177.5833	$177.58	$177.60	$177.60
Purchase #7	$176.53	8.464%	$191.4715	$191.47	$191.45	$191.50
7 purchase totals =	$980.26		$1,070.6192	$1,070.61	$1,070.60	$1,070.80