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	$134.87	7.242%	$144.6373	$144.64	$144.65	$144.60
Purchase #2	$203.90	9.408%	$223.0829	$223.08	$223.10	$223.10
Purchase #3	$119.65	3.116%	$123.3783	$123.38	$123.40	$123.40
Purchase #4	$211.30	13.588%	$240.0114	$240.01	$240.00	$240.00
Purchase #5	$40.81	7.275%	$43.7789	$43.78	$43.80	$43.80
Purchase #6	$214.25	11.801%	$239.5336	$239.53	$239.55	$239.50
Purchase #7	$46.46	12.213%	$52.1342	$52.13	$52.15	$52.10
7 purchase totals =	$971.24		$1,066.5566	$1,066.55	$1,066.65	$1,066.50