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	$225.81	10.498%	$249.5155	$249.52	$249.50	$249.50
Purchase #2	$133.91	8.422%	$145.1879	$145.19	$145.20	$145.20
Purchase #3	$103.92	9.812%	$114.1166	$114.12	$114.10	$114.10
Purchase #4	$96.34	3.667%	$99.8728	$99.87	$99.85	$99.90
Purchase #5	$161.69	6.243%	$171.7843	$171.78	$171.80	$171.80
Purchase #6	$20.61	7.136%	$22.0807	$22.08	$22.10	$22.10
Purchase #7	$121.40	8.593%	$131.8319	$131.83	$131.85	$131.80
7 purchase totals =	$863.68		$934.3897	$934.39	$934.40	$934.40