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	$77.85	12.431%	$87.5275	$87.53	$87.55	$87.50
Purchase #2	$41.28	6.324%	$43.8905	$43.89	$43.90	$43.90
Purchase #3	$250.83	8.719%	$272.6999	$272.70	$272.70	$272.70
Purchase #4	$146.67	3.865%	$152.3388	$152.34	$152.35	$152.30
Purchase #5	$98.27	3.737%	$101.9423	$101.94	$101.95	$101.90
Purchase #6	$244.56	8.281%	$264.812	$264.81	$264.80	$264.80
Purchase #7	$59.76	10.247%	$65.8836	$65.88	$65.90	$65.90
7 purchase totals =	$919.22		$989.0946	$989.09	$989.15	$989.00