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	$89.45	6.402%	$95.1766	$95.18	$95.20	$95.20
Purchase #2	$227.37	11.418%	$253.3311	$253.33	$253.35	$253.30
Purchase #3	$57.62	13.742%	$65.5381	$65.54	$65.55	$65.50
Purchase #4	$54.87	13.490%	$62.272	$62.27	$62.25	$62.30
Purchase #5	$35.51	5.137%	$37.3341	$37.33	$37.35	$37.30
Purchase #6	$225.72	6.403%	$240.1729	$240.17	$240.15	$240.20
Purchase #7	$47.86	7.722%	$51.5557	$51.56	$51.55	$51.60
7 purchase totals =	$738.40		$805.3805	$805.38	$805.40	$805.40