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	$125.46	11.509%	$139.8992	$139.90	$139.90	$139.90
Purchase #2	$57.34	6.392%	$61.0052	$61.01	$61.00	$61.00
Purchase #3	$32.81	8.263%	$35.5211	$35.52	$35.50	$35.50
Purchase #4	$199.99	5.684%	$211.3574	$211.36	$211.35	$211.40
Purchase #5	$150.43	11.323%	$167.4632	$167.46	$167.45	$167.50
Purchase #6	$169.88	6.570%	$181.0411	$181.04	$181.05	$181.00
Purchase #7	$167.98	10.430%	$185.5003	$185.50	$185.50	$185.50
7 purchase totals =	$903.89		$981.7875	$981.79	$981.75	$981.80