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	$162.29	4.182%	$169.077	$169.08	$169.10	$169.10
Purchase #2	$119.88	8.746%	$130.3647	$130.36	$130.35	$130.40
Purchase #3	$218.83	9.115%	$238.7764	$238.78	$238.80	$238.80
Purchase #4	$83.87	4.404%	$87.5636	$87.56	$87.55	$87.60
Purchase #5	$66.70	4.264%	$69.5441	$69.54	$69.55	$69.50
Purchase #6	$225.91	13.256%	$255.8566	$255.86	$255.85	$255.90
Purchase #7	$240.82	3.484%	$249.2102	$249.21	$249.20	$249.20
7 purchase totals =	$1,118.30		$1,200.3926	$1,200.39	$1,200.40	$1,200.50