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	$27.46	8.691%	$29.8465	$29.85	$29.85	$29.80
Purchase #2	$55.97	6.828%	$59.7916	$59.79	$59.80	$59.80
Purchase #3	$45.58	11.502%	$50.8226	$50.82	$50.80	$50.80
Purchase #4	$138.66	9.326%	$151.5914	$151.59	$151.60	$151.60
Purchase #5	$158.59	13.822%	$180.5103	$180.51	$180.50	$180.50
Purchase #6	$99.95	10.213%	$110.1579	$110.16	$110.15	$110.20
Purchase #7	$237.33	7.247%	$254.5293	$254.53	$254.55	$254.50
7 purchase totals =	$763.54		$837.2496	$837.25	$837.25	$837.20