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	$86.40	3.612%	$89.5208	$89.52	$89.50	$89.50
Purchase #2	$8.36	6.552%	$8.9077	$8.91	$8.90	$8.90
Purchase #3	$122.49	7.381%	$131.531	$131.53	$131.55	$131.50
Purchase #4	$71.61	6.243%	$76.0806	$76.08	$76.10	$76.10
Purchase #5	$75.83	12.751%	$85.4991	$85.50	$85.50	$85.50
Purchase #6	$128.40	12.534%	$144.4937	$144.49	$144.50	$144.50
Purchase #7	$13.37	5.752%	$14.139	$14.14	$14.15	$14.10
7 purchase totals =	$506.46		$550.1719	$550.17	$550.20	$550.10