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	$54.94	3.550%	$56.8904	$56.89	$56.90	$56.90
Purchase #2	$208.27	7.111%	$223.0801	$223.08	$223.10	$223.10
Purchase #3	$104.42	6.448%	$111.153	$111.15	$111.15	$111.20
Purchase #4	$163.75	10.677%	$181.2336	$181.23	$181.25	$181.20
Purchase #5	$166.51	13.789%	$189.4701	$189.47	$189.45	$189.50
Purchase #6	$169.91	3.334%	$175.5748	$175.57	$175.55	$175.60
Purchase #7	$241.83	12.618%	$272.3441	$272.34	$272.35	$272.30
7 purchase totals =	$1,109.63		$1,209.7461	$1,209.73	$1,209.75	$1,209.80