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	$20.85	7.380%	$22.3887	$22.39	$22.40	$22.40
Purchase #2	$245.66	11.817%	$274.6896	$274.69	$274.70	$274.70
Purchase #3	$18.25	12.571%	$20.5442	$20.54	$20.55	$20.50
Purchase #4	$107.69	4.411%	$112.4402	$112.44	$112.45	$112.40
Purchase #5	$194.57	3.195%	$200.7865	$200.79	$200.80	$200.80
Purchase #6	$64.57	9.775%	$70.8817	$70.88	$70.90	$70.90
Purchase #7	$129.47	6.188%	$137.4816	$137.48	$137.50	$137.50
7 purchase totals =	$781.06		$839.2125	$839.21	$839.30	$839.20