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	$30.94	3.675%	$32.077	$32.08	$32.10	$32.10
Purchase #2	$75.86	3.810%	$78.7503	$78.75	$78.75	$78.80
Purchase #3	$124.33	7.144%	$133.2121	$133.21	$133.20	$133.20
Purchase #4	$235.30	9.141%	$256.8088	$256.81	$256.80	$256.80
Purchase #5	$51.56	5.389%	$54.3386	$54.34	$54.35	$54.30
Purchase #6	$196.52	7.356%	$210.976	$210.98	$211.00	$211.00
Purchase #7	$140.90	4.789%	$147.6477	$147.65	$147.65	$147.60
7 purchase totals =	$855.41		$913.8105	$913.82	$913.85	$913.80