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	$26.63	10.403%	$29.4003	$29.40	$29.40	$29.40
Purchase #2	$248.29	8.170%	$268.5753	$268.58	$268.60	$268.60
Purchase #3	$72.91	7.857%	$78.6385	$78.64	$78.65	$78.60
Purchase #4	$140.61	7.775%	$151.5424	$151.54	$151.55	$151.50
Purchase #5	$8.72	6.134%	$9.2549	$9.25	$9.25	$9.30
Purchase #6	$145.50	11.586%	$162.3576	$162.36	$162.35	$162.40
Purchase #7	$78.51	10.380%	$86.6593	$86.66	$86.65	$86.70
7 purchase totals =	$721.17		$786.4283	$786.43	$786.45	$786.50