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	$168.92	6.606%	$180.0789	$180.08	$180.10	$180.10
Purchase #2	$131.40	3.191%	$135.593	$135.59	$135.60	$135.60
Purchase #3	$118.47	7.322%	$127.1444	$127.14	$127.15	$127.10
Purchase #4	$82.31	9.576%	$90.192	$90.19	$90.20	$90.20
Purchase #5	$77.38	6.683%	$82.5513	$82.55	$82.55	$82.60
Purchase #6	$169.41	7.305%	$181.7854	$181.79	$181.80	$181.80
Purchase #7	$32.91	8.561%	$35.7274	$35.73	$35.75	$35.70
7 purchase totals =	$780.80		$833.0724	$833.07	$833.15	$833.10