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	$133.67	4.404%	$139.5568	$139.56	$139.55	$139.60
Purchase #2	$23.29	13.872%	$26.5208	$26.52	$26.50	$26.50
Purchase #3	$137.40	13.165%	$155.4887	$155.49	$155.50	$155.50
Purchase #4	$106.52	5.686%	$112.5767	$112.58	$112.60	$112.60
Purchase #5	$105.82	7.260%	$113.5025	$113.50	$113.50	$113.50
Purchase #6	$84.68	7.234%	$90.8058	$90.81	$90.80	$90.80
Purchase #7	$50.49	7.257%	$54.1541	$54.15	$54.15	$54.20
7 purchase totals =	$641.87		$692.6054	$692.61	$692.60	$692.70