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	$40.50	12.320%	$45.4896	$45.49	$45.50	$45.50
Purchase #2	$127.98	9.721%	$140.4209	$140.42	$140.40	$140.40
Purchase #3	$95.92	3.265%	$99.0518	$99.05	$99.05	$99.10
Purchase #4	$228.97	13.192%	$259.1757	$259.18	$259.20	$259.20
Purchase #5	$210.28	3.825%	$218.3232	$218.32	$218.30	$218.30
Purchase #6	$183.32	4.458%	$191.4924	$191.49	$191.50	$191.50
Purchase #7	$183.41	12.274%	$205.9217	$205.92	$205.90	$205.90
7 purchase totals =	$1,070.38		$1,159.8753	$1,159.87	$1,159.85	$1,159.90