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	$82.87	9.504%	$90.746	$90.75	$90.75	$90.70
Purchase #2	$143.40	5.240%	$150.9142	$150.91	$150.90	$150.90
Purchase #3	$199.39	3.264%	$205.8981	$205.90	$205.90	$205.90
Purchase #4	$11.90	5.679%	$12.5758	$12.58	$12.60	$12.60
Purchase #5	$131.42	6.445%	$139.89	$139.89	$139.90	$139.90
Purchase #6	$37.31	9.449%	$40.8354	$40.84	$40.85	$40.80
Purchase #7	$124.96	8.173%	$135.173	$135.17	$135.15	$135.20
7 purchase totals =	$731.25		$776.0325	$776.04	$776.05	$776.00