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	$27.85	6.438%	$29.643	$29.64	$29.65	$29.60
Purchase #2	$102.96	5.289%	$108.4056	$108.41	$108.40	$108.40
Purchase #3	$57.95	3.315%	$59.871	$59.87	$59.85	$59.90
Purchase #4	$126.50	12.674%	$142.5326	$142.53	$142.55	$142.50
Purchase #5	$247.70	4.230%	$258.1777	$258.18	$258.20	$258.20
Purchase #6	$173.56	10.213%	$191.2857	$191.29	$191.30	$191.30
Purchase #7	$92.46	11.380%	$102.9819	$102.98	$103.00	$103.00
7 purchase totals =	$828.98		$892.8975	$892.90	$892.95	$892.90