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	$51.66	3.744%	$53.5942	$53.59	$53.60	$53.60
Purchase #2	$13.75	12.183%	$15.4252	$15.43	$15.45	$15.40
Purchase #3	$25.48	6.816%	$27.2167	$27.22	$27.20	$27.20
Purchase #4	$141.30	3.679%	$146.4984	$146.50	$146.50	$146.50
Purchase #5	$241.44	3.358%	$249.5476	$249.55	$249.55	$249.50
Purchase #6	$47.56	12.408%	$53.4612	$53.46	$53.45	$53.50
Purchase #7	$45.72	7.508%	$49.1527	$49.15	$49.15	$49.20
7 purchase totals =	$566.91		$594.8960	$594.90	$594.90	$594.90