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	$96.37	4.716%	$100.9148	$100.91	$100.90	$100.90
Purchase #2	$220.73	9.537%	$241.781	$241.78	$241.80	$241.80
Purchase #3	$92.28	4.260%	$96.2111	$96.21	$96.20	$96.20
Purchase #4	$109.72	12.802%	$123.7664	$123.77	$123.75	$123.80
Purchase #5	$16.67	12.273%	$18.7159	$18.72	$18.70	$18.70
Purchase #6	$126.81	8.245%	$137.2655	$137.27	$137.25	$137.30
Purchase #7	$162.60	13.748%	$184.9542	$184.95	$184.95	$185.00
7 purchase totals =	$825.18		$903.6089	$903.61	$903.55	$903.70