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	$147.29	6.120%	$156.3041	$156.30	$156.30	$156.30
Purchase #2	$125.40	5.702%	$132.5503	$132.55	$132.55	$132.60
Purchase #3	$25.52	8.168%	$27.6045	$27.60	$27.60	$27.60
Purchase #4	$35.29	3.263%	$36.4415	$36.44	$36.45	$36.40
Purchase #5	$109.29	4.795%	$114.5305	$114.53	$114.55	$114.50
Purchase #6	$74.80	5.468%	$78.8901	$78.89	$78.90	$78.90
Purchase #7	$52.41	4.678%	$54.8617	$54.86	$54.85	$54.90
7 purchase totals =	$570.00		$601.1827	$601.17	$601.20	$601.20