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	$85.88	9.448%	$93.9939	$93.99	$94.00	$94.00
Purchase #2	$67.83	12.649%	$76.4098	$76.41	$76.40	$76.40
Purchase #3	$137.51	4.742%	$144.0307	$144.03	$144.05	$144.00
Purchase #4	$74.38	10.728%	$82.3595	$82.36	$82.35	$82.40
Purchase #5	$105.63	6.719%	$112.7273	$112.73	$112.75	$112.70
Purchase #6	$184.60	6.660%	$196.8944	$196.89	$196.90	$196.90
Purchase #7	$232.42	7.744%	$250.4186	$250.42	$250.40	$250.40
7 purchase totals =	$888.25		$956.8342	$956.83	$956.85	$956.80