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	$110.45	7.834%	$119.1027	$119.10	$119.10	$119.10
Purchase #2	$104.57	3.298%	$108.0187	$108.02	$108.00	$108.00
Purchase #3	$237.62	9.238%	$259.5713	$259.57	$259.55	$259.60
Purchase #4	$39.58	7.380%	$42.501	$42.50	$42.50	$42.50
Purchase #5	$53.89	5.602%	$56.9089	$56.91	$56.90	$56.90
Purchase #6	$249.31	13.723%	$283.5228	$283.52	$283.50	$283.50
Purchase #7	$53.90	10.302%	$59.4528	$59.45	$59.45	$59.50
7 purchase totals =	$849.32		$929.0782	$929.07	$929.00	$929.10