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	$100.65	12.560%	$113.2916	$113.29	$113.30	$113.30
Purchase #2	$43.73	13.350%	$49.568	$49.57	$49.55	$49.60
Purchase #3	$20.33	6.666%	$21.6852	$21.69	$21.70	$21.70
Purchase #4	$209.80	3.683%	$217.5269	$217.53	$217.55	$217.50
Purchase #5	$62.75	10.835%	$69.549	$69.55	$69.55	$69.50
Purchase #6	$74.31	7.674%	$80.0125	$80.01	$80.00	$80.00
Purchase #7	$81.25	11.479%	$90.5767	$90.58	$90.60	$90.60
7 purchase totals =	$592.82		$642.2099	$642.22	$642.25	$642.20