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	$56.78	13.251%	$64.3039	$64.30	$64.30	$64.30
Purchase #2	$41.81	13.381%	$47.4046	$47.40	$47.40	$47.40
Purchase #3	$168.74	5.392%	$177.8385	$177.84	$177.85	$177.80
Purchase #4	$111.88	6.859%	$119.5538	$119.55	$119.55	$119.60
Purchase #5	$53.39	12.124%	$59.863	$59.86	$59.85	$59.90
Purchase #6	$35.49	8.472%	$38.4967	$38.50	$38.50	$38.50
Purchase #7	$169.33	9.401%	$185.2487	$185.25	$185.25	$185.20
7 purchase totals =	$637.42		$692.7092	$692.70	$692.70	$692.70