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	$36.30	6.732%	$38.7437	$38.74	$38.75	$38.70
Purchase #2	$216.99	5.684%	$229.3237	$229.32	$229.30	$229.30
Purchase #3	$91.38	13.403%	$103.6277	$103.63	$103.65	$103.60
Purchase #4	$153.25	13.439%	$173.8453	$173.85	$173.85	$173.80
Purchase #5	$6.70	6.351%	$7.1255	$7.13	$7.15	$7.10
Purchase #6	$29.78	10.517%	$32.912	$32.91	$32.90	$32.90
Purchase #7	$59.92	12.598%	$67.4687	$67.47	$67.45	$67.50
7 purchase totals =	$594.32		$653.0466	$653.05	$653.05	$652.90