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	$55.27	7.510%	$59.4208	$59.42	$59.40	$59.40
Purchase #2	$188.66	5.378%	$198.8061	$198.81	$198.80	$198.80
Purchase #3	$98.25	4.345%	$102.519	$102.52	$102.50	$102.50
Purchase #4	$101.96	6.694%	$108.7852	$108.79	$108.80	$108.80
Purchase #5	$19.69	11.369%	$21.9286	$21.93	$21.95	$21.90
Purchase #6	$24.87	5.834%	$26.3209	$26.32	$26.30	$26.30
Purchase #7	$39.68	5.544%	$41.8799	$41.88	$41.90	$41.90
7 purchase totals =	$528.38		$559.6605	$559.67	$559.65	$559.60