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	$33.71	10.324%	$37.1902	$37.19	$37.20	$37.20
Purchase #2	$40.90	6.472%	$43.547	$43.55	$43.55	$43.50
Purchase #3	$132.77	4.855%	$139.216	$139.22	$139.20	$139.20
Purchase #4	$32.97	12.328%	$37.0345	$37.03	$37.05	$37.00
Purchase #5	$23.36	10.125%	$25.7252	$25.73	$25.75	$25.70
Purchase #6	$78.76	5.835%	$83.3556	$83.36	$83.35	$83.40
Purchase #7	$16.88	11.207%	$18.7717	$18.77	$18.75	$18.80
7 purchase totals =	$359.35		$384.8402	$384.85	$384.85	$384.80