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	$26.60	5.338%	$28.0199	$28.02	$28.00	$28.00
Purchase #2	$163.46	13.410%	$185.38	$185.38	$185.40	$185.40
Purchase #3	$53.69	5.824%	$56.8169	$56.82	$56.80	$56.80
Purchase #4	$78.56	9.809%	$86.266	$86.27	$86.25	$86.30
Purchase #5	$26.70	3.141%	$27.5386	$27.54	$27.55	$27.50
Purchase #6	$65.72	10.123%	$72.3728	$72.37	$72.35	$72.40
Purchase #7	$190.59	3.649%	$197.5446	$197.54	$197.55	$197.50
7 purchase totals =	$605.32		$653.9388	$653.94	$653.90	$653.90