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	$147.64	9.744%	$162.026	$162.03	$162.05	$162.00
Purchase #2	$248.84	12.323%	$279.5046	$279.50	$279.50	$279.50
Purchase #3	$116.60	10.528%	$128.8756	$128.88	$128.90	$128.90
Purchase #4	$10.56	13.667%	$12.0032	$12.00	$12.00	$12.00
Purchase #5	$34.40	9.311%	$37.603	$37.60	$37.60	$37.60
Purchase #6	$81.38	4.483%	$85.0283	$85.03	$85.05	$85.00
Purchase #7	$112.94	10.153%	$124.4068	$124.41	$124.40	$124.40
7 purchase totals =	$752.36		$829.4475	$829.45	$829.50	$829.40