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	$241.75	12.445%	$271.8358	$271.84	$271.85	$271.80
Purchase #2	$201.38	10.445%	$222.4141	$222.41	$222.40	$222.40
Purchase #3	$18.80	9.853%	$20.6524	$20.65	$20.65	$20.70
Purchase #4	$58.99	3.174%	$60.8623	$60.86	$60.85	$60.90
Purchase #5	$30.70	3.868%	$31.8875	$31.89	$31.90	$31.90
Purchase #6	$196.90	10.606%	$217.7832	$217.78	$217.80	$217.80
Purchase #7	$12.39	4.457%	$12.9422	$12.94	$12.95	$12.90
7 purchase totals =	$760.91		$838.3775	$838.37	$838.40	$838.40