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	$220.94	6.143%	$234.5123	$234.51	$234.50	$234.50
Purchase #2	$145.32	12.304%	$163.2002	$163.20	$163.20	$163.20
Purchase #3	$138.37	5.618%	$146.1436	$146.14	$146.15	$146.10
Purchase #4	$50.61	9.643%	$55.4903	$55.49	$55.50	$55.50
Purchase #5	$161.87	10.520%	$178.8987	$178.90	$178.90	$178.90
Purchase #6	$47.96	9.480%	$52.5066	$52.51	$52.50	$52.50
Purchase #7	$174.47	6.541%	$185.8821	$185.88	$185.90	$185.90
7 purchase totals =	$939.54		$1,016.6338	$1,016.63	$1,016.65	$1,016.60