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	$122.28	9.479%	$133.8709	$133.87	$133.85	$133.90
Purchase #2	$105.80	3.597%	$109.6056	$109.61	$109.60	$109.60
Purchase #3	$37.62	11.304%	$41.8726	$41.87	$41.85	$41.90
Purchase #4	$148.75	13.318%	$168.5605	$168.56	$168.55	$168.60
Purchase #5	$58.95	12.769%	$66.4773	$66.48	$66.50	$66.50
Purchase #6	$50.93	3.223%	$52.5715	$52.57	$52.55	$52.60
Purchase #7	$69.45	12.112%	$77.8618	$77.86	$77.85	$77.90
7 purchase totals =	$593.78		$650.8202	$650.82	$650.75	$651.00