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	$35.39	3.450%	$36.611	$36.61	$36.60	$36.60
Purchase #2	$155.94	9.257%	$170.3754	$170.38	$170.40	$170.40
Purchase #3	$71.86	8.565%	$78.0148	$78.01	$78.00	$78.00
Purchase #4	$51.38	5.810%	$54.3652	$54.37	$54.35	$54.40
Purchase #5	$138.94	7.612%	$149.5161	$149.52	$149.50	$149.50
Purchase #6	$30.36	6.113%	$32.2159	$32.22	$32.20	$32.20
Purchase #7	$51.78	7.360%	$55.591	$55.59	$55.60	$55.60
7 purchase totals =	$535.65		$576.6894	$576.70	$576.65	$576.70