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	$249.71	6.528%	$266.0111	$266.01	$266.00	$266.00
Purchase #2	$49.75	10.548%	$54.9976	$55.00	$55.00	$55.00
Purchase #3	$115.80	13.144%	$131.0208	$131.02	$131.00	$131.00
Purchase #4	$185.51	6.423%	$197.4253	$197.43	$197.45	$197.40
Purchase #5	$166.46	9.681%	$182.575	$182.58	$182.60	$182.60
Purchase #6	$85.74	4.138%	$89.2879	$89.29	$89.30	$89.30
Purchase #7	$126.80	12.419%	$142.5473	$142.55	$142.55	$142.50
7 purchase totals =	$979.77		$1,063.8650	$1,063.88	$1,063.90	$1,063.80