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	$38.69	3.120%	$39.8971	$39.90	$39.90	$39.90
Purchase #2	$22.45	10.337%	$24.7707	$24.77	$24.75	$24.80
Purchase #3	$201.73	8.693%	$219.2664	$219.27	$219.25	$219.30
Purchase #4	$108.53	13.492%	$123.1729	$123.17	$123.15	$123.20
Purchase #5	$187.43	10.213%	$206.5722	$206.57	$206.55	$206.60
Purchase #6	$239.47	4.535%	$250.33	$250.33	$250.35	$250.30
Purchase #7	$121.61	8.451%	$131.8873	$131.89	$131.90	$131.90
7 purchase totals =	$919.91		$995.8966	$995.90	$995.85	$996.00