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	$12.50	6.323%	$13.2904	$13.29	$13.30	$13.30
Purchase #2	$239.47	4.232%	$249.6044	$249.60	$249.60	$249.60
Purchase #3	$120.69	13.500%	$136.9832	$136.98	$137.00	$137.00
Purchase #4	$70.87	4.260%	$73.8891	$73.89	$73.90	$73.90
Purchase #5	$217.89	7.621%	$234.4954	$234.50	$234.50	$234.50
Purchase #6	$238.63	3.467%	$246.9033	$246.90	$246.90	$246.90
Purchase #7	$59.73	9.366%	$65.3243	$65.32	$65.30	$65.30
7 purchase totals =	$959.78		$1,020.4901	$1,020.48	$1,020.50	$1,020.50