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	$128.53	11.862%	$143.7762	$143.78	$143.80	$143.80
Purchase #2	$27.86	6.233%	$29.5965	$29.60	$29.60	$29.60
Purchase #3	$136.45	7.582%	$146.7956	$146.80	$146.80	$146.80
Purchase #4	$45.90	13.655%	$52.1676	$52.17	$52.15	$52.20
Purchase #5	$119.62	7.201%	$128.2338	$128.23	$128.25	$128.20
Purchase #6	$75.62	13.505%	$85.8325	$85.83	$85.85	$85.80
Purchase #7	$59.83	10.751%	$66.2623	$66.26	$66.25	$66.30
7 purchase totals =	$593.81		$652.6645	$652.67	$652.70	$652.70