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	$249.64	7.601%	$268.6151	$268.62	$268.60	$268.60
Purchase #2	$158.28	13.842%	$180.1891	$180.19	$180.20	$180.20
Purchase #3	$42.55	8.527%	$46.1782	$46.18	$46.20	$46.20
Purchase #4	$30.97	5.849%	$32.7814	$32.78	$32.80	$32.80
Purchase #5	$127.71	7.453%	$137.2282	$137.23	$137.25	$137.20
Purchase #6	$78.81	8.605%	$85.5916	$85.59	$85.60	$85.60
Purchase #7	$35.96	12.103%	$40.3122	$40.31	$40.30	$40.30
7 purchase totals =	$723.92		$790.8958	$790.90	$790.95	$790.90