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	$149.79	12.713%	$168.8328	$168.83	$168.85	$168.80
Purchase #2	$148.67	10.506%	$164.2893	$164.29	$164.30	$164.30
Purchase #3	$97.98	10.592%	$108.358	$108.36	$108.35	$108.40
Purchase #4	$110.99	5.563%	$117.1644	$117.16	$117.15	$117.20
Purchase #5	$27.33	7.867%	$29.4801	$29.48	$29.50	$29.50
Purchase #6	$91.94	13.658%	$104.4972	$104.50	$104.50	$104.50
Purchase #7	$91.67	4.120%	$95.4468	$95.45	$95.45	$95.40
7 purchase totals =	$718.37		$788.0686	$788.07	$788.10	$788.10