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	$9.82	3.684%	$10.1818	$10.18	$10.20	$10.20
Purchase #2	$86.84	4.341%	$90.6097	$90.61	$90.60	$90.60
Purchase #3	$33.83	3.674%	$35.0729	$35.07	$35.05	$35.10
Purchase #4	$78.90	6.359%	$83.9173	$83.92	$83.90	$83.90
Purchase #5	$7.80	3.539%	$8.076	$8.08	$8.10	$8.10
Purchase #6	$6.99	9.282%	$7.6388	$7.64	$7.65	$7.60
Purchase #7	$83.91	7.726%	$90.3929	$90.39	$90.40	$90.40
7 purchase totals =	$308.09		$325.8894	$325.89	$325.90	$325.90