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	$34.90	3.626%	$36.1655	$36.17	$36.15	$36.20
Purchase #2	$186.64	12.203%	$209.4157	$209.42	$209.40	$209.40
Purchase #3	$98.85	4.662%	$103.4584	$103.46	$103.45	$103.50
Purchase #4	$212.38	8.710%	$230.8783	$230.88	$230.90	$230.90
Purchase #5	$46.96	3.275%	$48.4979	$48.50	$48.50	$48.50
Purchase #6	$84.88	13.544%	$96.3761	$96.38	$96.40	$96.40
Purchase #7	$111.76	6.863%	$119.4301	$119.43	$119.45	$119.40
7 purchase totals =	$776.37		$844.2220	$844.24	$844.25	$844.30