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	$82.44	6.403%	$87.7186	$87.72	$87.70	$87.70
Purchase #2	$203.71	5.510%	$214.9344	$214.93	$214.95	$214.90
Purchase #3	$37.34	8.424%	$40.4855	$40.49	$40.50	$40.50
Purchase #4	$162.61	12.207%	$182.4598	$182.46	$182.45	$182.50
Purchase #5	$71.67	6.594%	$76.3959	$76.40	$76.40	$76.40
Purchase #6	$90.88	10.721%	$100.6232	$100.62	$100.60	$100.60
Purchase #7	$188.50	4.108%	$196.2436	$196.24	$196.25	$196.20
7 purchase totals =	$837.15		$898.8610	$898.86	$898.85	$898.80