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	$171.58	4.168%	$178.7315	$178.73	$178.75	$178.70
Purchase #2	$75.43	13.647%	$85.7239	$85.72	$85.70	$85.70
Purchase #3	$12.60	5.627%	$13.309	$13.31	$13.30	$13.30
Purchase #4	$147.28	5.285%	$155.0637	$155.06	$155.05	$155.10
Purchase #5	$164.28	4.363%	$171.4475	$171.45	$171.45	$171.40
Purchase #6	$66.70	7.712%	$71.8439	$71.84	$71.85	$71.80
Purchase #7	$140.64	12.602%	$158.3635	$158.36	$158.35	$158.40
7 purchase totals =	$778.51		$834.4830	$834.47	$834.45	$834.40