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	$96.71	3.842%	$100.4256	$100.43	$100.45	$100.40
Purchase #2	$220.77	10.578%	$244.1231	$244.12	$244.10	$244.10
Purchase #3	$95.53	7.529%	$102.7225	$102.72	$102.70	$102.70
Purchase #4	$29.28	8.175%	$31.6736	$31.67	$31.65	$31.70
Purchase #5	$180.81	8.509%	$196.1951	$196.20	$196.20	$196.20
Purchase #6	$109.71	5.300%	$115.5246	$115.52	$115.50	$115.50
Purchase #7	$230.71	5.785%	$244.0566	$244.06	$244.05	$244.10
7 purchase totals =	$963.52		$1,034.7211	$1,034.72	$1,034.65	$1,034.70