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	$134.57	3.380%	$139.1185	$139.12	$139.10	$139.10
Purchase #2	$84.31	7.719%	$90.8179	$90.82	$90.80	$90.80
Purchase #3	$125.51	11.805%	$140.3265	$140.33	$140.35	$140.30
Purchase #4	$127.64	8.575%	$138.5851	$138.59	$138.60	$138.60
Purchase #5	$140.43	5.694%	$148.4261	$148.43	$148.45	$148.40
Purchase #6	$119.48	13.838%	$136.0136	$136.01	$136.00	$136.00
Purchase #7	$38.42	3.281%	$39.6806	$39.68	$39.70	$39.70
7 purchase totals =	$770.36		$832.9683	$832.98	$833.00	$832.90