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	$13.40	11.345%	$14.9202	$14.92	$14.90	$14.90
Purchase #2	$101.89	4.688%	$106.6666	$106.67	$106.65	$106.70
Purchase #3	$18.63	8.787%	$20.267	$20.27	$20.25	$20.30
Purchase #4	$128.45	13.601%	$145.9205	$145.92	$145.90	$145.90
Purchase #5	$55.64	12.280%	$62.4726	$62.47	$62.45	$62.50
Purchase #6	$232.52	10.280%	$256.4231	$256.42	$256.40	$256.40
Purchase #7	$81.69	7.627%	$87.9205	$87.92	$87.90	$87.90
7 purchase totals =	$632.22		$694.5905	$694.59	$694.45	$694.60