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	$68.55	11.755%	$76.6081	$76.61	$76.60	$76.60
Purchase #2	$117.31	5.164%	$123.3679	$123.37	$123.35	$123.40
Purchase #3	$224.25	13.383%	$254.2614	$254.26	$254.25	$254.30
Purchase #4	$55.94	6.383%	$59.5107	$59.51	$59.50	$59.50
Purchase #5	$27.59	3.175%	$28.466	$28.47	$28.45	$28.50
Purchase #6	$131.89	4.226%	$137.4637	$137.46	$137.45	$137.50
Purchase #7	$191.44	9.270%	$209.1865	$209.19	$209.20	$209.20
7 purchase totals =	$816.97		$888.8643	$888.87	$888.80	$889.00