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	$220.63	6.172%	$234.2473	$234.25	$234.25	$234.20
Purchase #2	$176.58	13.160%	$199.8179	$199.82	$199.80	$199.80
Purchase #3	$117.72	5.269%	$123.9227	$123.92	$123.90	$123.90
Purchase #4	$119.50	11.810%	$133.613	$133.61	$133.60	$133.60
Purchase #5	$14.52	12.666%	$16.3591	$16.36	$16.35	$16.40
Purchase #6	$40.29	6.336%	$42.8428	$42.84	$42.85	$42.80
Purchase #7	$129.85	9.718%	$142.4688	$142.47	$142.45	$142.50
7 purchase totals =	$819.09		$893.2716	$893.27	$893.20	$893.20