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	$163.32	9.762%	$179.2633	$179.26	$179.25	$179.30
Purchase #2	$159.56	7.107%	$170.8999	$170.90	$170.90	$170.90
Purchase #3	$144.61	13.566%	$164.2278	$164.23	$164.25	$164.20
Purchase #4	$34.69	10.766%	$38.4247	$38.42	$38.40	$38.40
Purchase #5	$55.67	10.380%	$61.4485	$61.45	$61.45	$61.40
Purchase #6	$31.65	3.673%	$32.8125	$32.81	$32.80	$32.80
Purchase #7	$83.95	13.416%	$95.2127	$95.21	$95.20	$95.20
7 purchase totals =	$673.45		$742.2894	$742.28	$742.25	$742.20