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	$21.87	5.801%	$23.1387	$23.14	$23.15	$23.10
Purchase #2	$145.92	3.358%	$150.82	$150.82	$150.80	$150.80
Purchase #3	$149.66	7.658%	$161.121	$161.12	$161.10	$161.10
Purchase #4	$61.69	4.216%	$64.2909	$64.29	$64.30	$64.30
Purchase #5	$113.47	5.159%	$119.3239	$119.32	$119.30	$119.30
Purchase #6	$111.57	7.191%	$119.593	$119.59	$119.60	$119.60
Purchase #7	$35.34	7.576%	$38.0174	$38.02	$38.00	$38.00
7 purchase totals =	$639.52		$676.3049	$676.30	$676.25	$676.20