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	$235.92	5.667%	$249.2896	$249.29	$249.30	$249.30
Purchase #2	$35.75	10.332%	$39.4437	$39.44	$39.45	$39.40
Purchase #3	$27.69	12.636%	$31.1889	$31.19	$31.20	$31.20
Purchase #4	$131.80	6.589%	$140.4843	$140.48	$140.50	$140.50
Purchase #5	$99.60	12.182%	$111.7333	$111.73	$111.75	$111.70
Purchase #6	$127.96	10.681%	$141.6274	$141.63	$141.65	$141.60
Purchase #7	$81.42	13.606%	$92.498	$92.50	$92.50	$92.50
7 purchase totals =	$740.14		$806.2652	$806.26	$806.35	$806.20