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	$230.26	12.849%	$259.8461	$259.85	$259.85	$259.80
Purchase #2	$222.28	12.484%	$250.0294	$250.03	$250.05	$250.00
Purchase #3	$65.93	11.558%	$73.5502	$73.55	$73.55	$73.60
Purchase #4	$36.62	4.520%	$38.2752	$38.28	$38.30	$38.30
Purchase #5	$13.63	9.461%	$14.9195	$14.92	$14.90	$14.90
Purchase #6	$73.47	6.669%	$78.3697	$78.37	$78.35	$78.40
Purchase #7	$234.88	12.347%	$263.8806	$263.88	$263.90	$263.90
7 purchase totals =	$877.07		$978.8707	$978.88	$978.90	$978.90