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	$81.44	5.718%	$86.0967	$86.10	$86.10	$86.10
Purchase #2	$47.76	7.485%	$51.3348	$51.33	$51.35	$51.30
Purchase #3	$96.96	3.615%	$100.4651	$100.47	$100.45	$100.50
Purchase #4	$173.50	9.553%	$190.0745	$190.07	$190.05	$190.10
Purchase #5	$74.93	9.382%	$81.9599	$81.96	$81.95	$82.00
Purchase #6	$118.74	11.286%	$132.141	$132.14	$132.15	$132.10
Purchase #7	$53.78	10.138%	$59.2322	$59.23	$59.25	$59.20
7 purchase totals =	$647.11		$701.3042	$701.30	$701.30	$701.30