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	$100.27	13.571%	$113.8776	$113.88	$113.90	$113.90
Purchase #2	$87.29	4.108%	$90.8759	$90.88	$90.90	$90.90
Purchase #3	$116.32	10.625%	$128.679	$128.68	$128.70	$128.70
Purchase #4	$18.50	9.340%	$20.2279	$20.23	$20.25	$20.20
Purchase #5	$211.86	12.158%	$237.6179	$237.62	$237.60	$237.60
Purchase #6	$17.62	9.183%	$19.238	$19.24	$19.25	$19.20
Purchase #7	$159.63	12.714%	$179.9254	$179.93	$179.95	$179.90
7 purchase totals =	$711.49		$790.4417	$790.46	$790.55	$790.40