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	$8.35	13.638%	$9.4888	$9.49	$9.50	$9.50
Purchase #2	$38.58	12.694%	$43.4773	$43.48	$43.50	$43.50
Purchase #3	$211.58	5.738%	$223.7205	$223.72	$223.70	$223.70
Purchase #4	$219.59	9.107%	$239.5881	$239.59	$239.60	$239.60
Purchase #5	$47.32	7.360%	$50.8028	$50.80	$50.80	$50.80
Purchase #6	$37.33	13.432%	$42.3442	$42.34	$42.35	$42.30
Purchase #7	$75.45	9.717%	$82.7815	$82.78	$82.80	$82.80
7 purchase totals =	$638.20		$692.2032	$692.20	$692.25	$692.20