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	$43.83	8.260%	$47.4504	$47.45	$47.45	$47.50
Purchase #2	$142.96	8.171%	$154.6413	$154.64	$154.65	$154.60
Purchase #3	$95.27	10.717%	$105.4801	$105.48	$105.50	$105.50
Purchase #4	$32.48	8.134%	$35.1219	$35.12	$35.10	$35.10
Purchase #5	$96.86	7.656%	$104.2756	$104.28	$104.30	$104.30
Purchase #6	$6.77	8.847%	$7.3689	$7.37	$7.35	$7.40
Purchase #7	$145.85	12.855%	$164.599	$164.60	$164.60	$164.60
7 purchase totals =	$564.02		$618.9372	$618.94	$618.95	$619.00