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	$6.33	10.249%	$6.9788	$6.98	$7.00	$7.00
Purchase #2	$63.29	13.192%	$71.6392	$71.64	$71.65	$71.60
Purchase #3	$230.87	13.746%	$262.6054	$262.61	$262.60	$262.60
Purchase #4	$75.53	12.406%	$84.9003	$84.90	$84.90	$84.90
Purchase #5	$204.93	6.545%	$218.3427	$218.34	$218.35	$218.30
Purchase #6	$247.70	3.183%	$255.5843	$255.58	$255.60	$255.60
Purchase #7	$90.44	13.640%	$102.776	$102.78	$102.80	$102.80
7 purchase totals =	$919.09		$1,002.8267	$1,002.83	$1,002.90	$1,002.80