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	$27.41	5.164%	$28.8255	$28.83	$28.85	$28.80
Purchase #2	$37.52	6.298%	$39.883	$39.88	$39.90	$39.90
Purchase #3	$131.72	3.330%	$136.1063	$136.11	$136.10	$136.10
Purchase #4	$179.57	5.766%	$189.924	$189.92	$189.90	$189.90
Purchase #5	$97.97	4.518%	$102.3963	$102.40	$102.40	$102.40
Purchase #6	$144.41	8.527%	$156.7238	$156.72	$156.70	$156.70
Purchase #7	$101.34	10.557%	$112.0385	$112.04	$112.05	$112.00
7 purchase totals =	$719.94		$765.8974	$765.90	$765.90	$765.80