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	$127.29	9.374%	$139.2222	$139.22	$139.20	$139.20
Purchase #2	$62.48	4.229%	$65.1223	$65.12	$65.10	$65.10
Purchase #3	$35.69	13.405%	$40.4742	$40.47	$40.45	$40.50
Purchase #4	$144.35	5.310%	$152.015	$152.02	$152.00	$152.00
Purchase #5	$235.39	12.840%	$265.6141	$265.61	$265.60	$265.60
Purchase #6	$11.50	9.358%	$12.5762	$12.58	$12.60	$12.60
Purchase #7	$94.32	7.646%	$101.5317	$101.53	$101.55	$101.50
7 purchase totals =	$711.02		$776.5557	$776.55	$776.50	$776.50