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	$38.79	4.305%	$40.4599	$40.46	$40.45	$40.50
Purchase #2	$45.39	3.254%	$46.867	$46.87	$46.85	$46.90
Purchase #3	$85.49	11.617%	$95.4214	$95.42	$95.40	$95.40
Purchase #4	$18.54	10.213%	$20.4335	$20.43	$20.45	$20.40
Purchase #5	$84.89	13.171%	$96.0709	$96.07	$96.05	$96.10
Purchase #6	$222.80	7.527%	$239.5702	$239.57	$239.55	$239.60
Purchase #7	$236.41	5.558%	$249.5497	$249.55	$249.55	$249.50
7 purchase totals =	$732.31		$788.3726	$788.37	$788.30	$788.40