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	$202.81	11.550%	$226.2346	$226.23	$226.25	$226.20
Purchase #2	$49.47	4.331%	$51.6125	$51.61	$51.60	$51.60
Purchase #3	$7.48	5.530%	$7.8936	$7.89	$7.90	$7.90
Purchase #4	$49.43	10.362%	$54.5519	$54.55	$54.55	$54.60
Purchase #5	$197.68	12.414%	$222.22	$222.22	$222.20	$222.20
Purchase #6	$19.27	12.531%	$21.6847	$21.68	$21.70	$21.70
Purchase #7	$73.25	11.103%	$81.3829	$81.38	$81.40	$81.40
7 purchase totals =	$599.39		$665.5802	$665.56	$665.60	$665.60