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	$51.72	5.407%	$54.5165	$54.52	$54.50	$54.50
Purchase #2	$231.28	7.492%	$248.6075	$248.61	$248.60	$248.60
Purchase #3	$94.73	8.242%	$102.5376	$102.54	$102.55	$102.50
Purchase #4	$245.46	5.722%	$259.5052	$259.51	$259.50	$259.50
Purchase #5	$123.60	10.383%	$136.4334	$136.43	$136.45	$136.40
Purchase #6	$84.31	7.345%	$90.5026	$90.50	$90.50	$90.50
Purchase #7	$183.30	3.204%	$189.1729	$189.17	$189.15	$189.20
7 purchase totals =	$1,014.40		$1,081.2757	$1,081.28	$1,081.25	$1,081.20