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	$31.78	3.401%	$32.8608	$32.86	$32.85	$32.90
Purchase #2	$84.38	11.201%	$93.8314	$93.83	$93.85	$93.80
Purchase #3	$114.43	6.374%	$121.7238	$121.72	$121.70	$121.70
Purchase #4	$167.59	13.162%	$189.6482	$189.65	$189.65	$189.60
Purchase #5	$17.40	9.133%	$18.9891	$18.99	$19.00	$19.00
Purchase #6	$55.58	6.373%	$59.1221	$59.12	$59.10	$59.10
Purchase #7	$80.58	12.250%	$90.4511	$90.45	$90.45	$90.50
7 purchase totals =	$551.74		$606.6265	$606.62	$606.60	$606.60