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	$227.98	4.509%	$238.2596	$238.26	$238.25	$238.30
Purchase #2	$222.64	11.310%	$247.8206	$247.82	$247.80	$247.80
Purchase #3	$243.71	8.868%	$265.3222	$265.32	$265.30	$265.30
Purchase #4	$95.70	7.588%	$102.9617	$102.96	$102.95	$103.00
Purchase #5	$106.82	4.390%	$111.5094	$111.51	$111.50	$111.50
Purchase #6	$139.80	11.773%	$156.2587	$156.26	$156.25	$156.30
Purchase #7	$62.70	8.139%	$67.8032	$67.80	$67.80	$67.80
7 purchase totals =	$1,099.35		$1,189.9354	$1,189.93	$1,189.85	$1,190.00