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	$93.45	4.729%	$97.8693	$97.87	$97.85	$97.90
Purchase #2	$216.37	6.537%	$230.5141	$230.51	$230.50	$230.50
Purchase #3	$87.74	3.572%	$90.8741	$90.87	$90.85	$90.90
Purchase #4	$90.58	13.804%	$103.0837	$103.08	$103.10	$103.10
Purchase #5	$26.25	10.467%	$28.9976	$29.00	$29.00	$29.00
Purchase #6	$200.88	4.454%	$209.8272	$209.83	$209.85	$209.80
Purchase #7	$16.64	13.326%	$18.8574	$18.86	$18.85	$18.90
7 purchase totals =	$731.91		$780.0234	$780.02	$780.00	$780.10