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	$121.75	5.606%	$128.5753	$128.58	$128.60	$128.60
Purchase #2	$94.61	8.629%	$102.7739	$102.77	$102.75	$102.80
Purchase #3	$31.80	3.470%	$32.9035	$32.90	$32.90	$32.90
Purchase #4	$219.30	13.259%	$248.377	$248.38	$248.40	$248.40
Purchase #5	$164.97	5.192%	$173.5352	$173.54	$173.55	$173.50
Purchase #6	$157.27	5.754%	$166.3193	$166.32	$166.30	$166.30
Purchase #7	$36.96	9.334%	$40.4098	$40.41	$40.40	$40.40
7 purchase totals =	$826.66		$892.8940	$892.90	$892.90	$892.90