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	$125.29	10.696%	$138.691	$138.69	$138.70	$138.70
Purchase #2	$80.60	12.748%	$90.8749	$90.87	$90.85	$90.90
Purchase #3	$185.67	9.508%	$203.3235	$203.32	$203.30	$203.30
Purchase #4	$112.35	5.130%	$118.1136	$118.11	$118.10	$118.10
Purchase #5	$65.83	11.249%	$73.2352	$73.24	$73.25	$73.20
Purchase #6	$80.85	11.667%	$90.2828	$90.28	$90.30	$90.30
Purchase #7	$42.26	8.237%	$45.741	$45.74	$45.75	$45.70
7 purchase totals =	$692.85		$760.2620	$760.25	$760.25	$760.20