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	$25.56	8.791%	$27.807	$27.81	$27.80	$27.80
Purchase #2	$75.45	6.483%	$80.3414	$80.34	$80.35	$80.30
Purchase #3	$67.94	6.834%	$72.583	$72.58	$72.60	$72.60
Purchase #4	$82.61	5.711%	$87.3279	$87.33	$87.35	$87.30
Purchase #5	$189.56	7.821%	$204.3855	$204.39	$204.40	$204.40
Purchase #6	$15.99	9.452%	$17.5014	$17.50	$17.50	$17.50
Purchase #7	$117.45	8.547%	$127.4885	$127.49	$127.50	$127.50
7 purchase totals =	$574.56		$617.4347	$617.44	$617.50	$617.40