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	$131.78	7.189%	$141.2537	$141.25	$141.25	$141.30
Purchase #2	$204.55	9.213%	$223.3952	$223.40	$223.40	$223.40
Purchase #3	$248.53	12.566%	$279.7603	$279.76	$279.75	$279.80
Purchase #4	$55.92	5.807%	$59.1673	$59.17	$59.15	$59.20
Purchase #5	$183.57	11.555%	$204.7815	$204.78	$204.80	$204.80
Purchase #6	$69.65	12.666%	$78.4719	$78.47	$78.45	$78.50
Purchase #7	$28.94	13.329%	$32.7974	$32.80	$32.80	$32.80
7 purchase totals =	$922.94		$1,019.6273	$1,019.63	$1,019.60	$1,019.80