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	5.508%	$31.5574	$31.56	$31.55	$31.60
Purchase #2	$129.41	8.707%	$140.6777	$140.68	$140.70	$140.70
Purchase #3	$181.59	4.377%	$189.5382	$189.54	$189.55	$189.50
Purchase #4	$148.89	10.785%	$164.9478	$164.95	$164.95	$164.90
Purchase #5	$87.29	4.194%	$90.9509	$90.95	$90.95	$91.00
Purchase #6	$90.98	12.554%	$102.4016	$102.40	$102.40	$102.40
Purchase #7	$43.78	3.118%	$45.1451	$45.15	$45.15	$45.10
7 purchase totals =	$711.85		$765.2187	$765.23	$765.25	$765.20