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	$29.91	12.434%	$33.629	$33.63	$33.65	$33.60
Purchase #2	$82.42	6.596%	$87.8564	$87.86	$87.85	$87.90
Purchase #3	$109.49	9.109%	$119.4634	$119.46	$119.45	$119.50
Purchase #4	$38.47	6.416%	$40.9382	$40.94	$40.95	$40.90
Purchase #5	$169.46	11.159%	$188.37	$188.37	$188.35	$188.40
Purchase #6	$40.60	12.650%	$45.7359	$45.74	$45.75	$45.70
Purchase #7	$90.71	10.235%	$99.9942	$99.99	$100.00	$100.00
7 purchase totals =	$561.06		$615.9871	$615.99	$616.00	$616.00