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	$81.68	9.352%	$89.3187	$89.32	$89.30	$89.30
Purchase #2	$66.81	6.245%	$70.9823	$70.98	$71.00	$71.00
Purchase #3	$126.38	6.723%	$134.8765	$134.88	$134.90	$134.90
Purchase #4	$170.87	11.731%	$190.9148	$190.91	$190.90	$190.90
Purchase #5	$98.68	7.123%	$105.709	$105.71	$105.70	$105.70
Purchase #6	$72.95	7.648%	$78.5292	$78.53	$78.55	$78.50
Purchase #7	$231.85	5.811%	$245.3228	$245.32	$245.30	$245.30
7 purchase totals =	$849.22		$915.6533	$915.65	$915.65	$915.60