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	$35.91	12.360%	$40.3485	$40.35	$40.35	$40.30
Purchase #2	$105.78	3.217%	$109.1829	$109.18	$109.20	$109.20
Purchase #3	$104.74	7.527%	$112.6238	$112.62	$112.60	$112.60
Purchase #4	$81.36	5.155%	$85.5541	$85.55	$85.55	$85.60
Purchase #5	$240.38	5.205%	$252.8918	$252.89	$252.90	$252.90
Purchase #6	$130.89	11.384%	$145.7905	$145.79	$145.80	$145.80
Purchase #7	$45.58	13.741%	$51.8431	$51.84	$51.85	$51.80
7 purchase totals =	$744.64		$798.2347	$798.22	$798.25	$798.20