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	$115.55	6.558%	$123.1278	$123.13	$123.15	$123.10
Purchase #2	$56.90	7.606%	$61.2278	$61.23	$61.25	$61.20
Purchase #3	$181.46	9.268%	$198.2777	$198.28	$198.30	$198.30
Purchase #4	$203.55	3.616%	$210.9104	$210.91	$210.90	$210.90
Purchase #5	$106.52	4.251%	$111.0482	$111.05	$111.05	$111.00
Purchase #6	$115.26	5.387%	$121.4691	$121.47	$121.45	$121.50
Purchase #7	$156.54	11.457%	$174.4748	$174.47	$174.45	$174.50
7 purchase totals =	$935.78		$1,000.5358	$1,000.54	$1,000.55	$1,000.50