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	$86.51	3.210%	$89.287	$89.29	$89.30	$89.30
Purchase #2	$208.66	9.544%	$228.5745	$228.57	$228.55	$228.60
Purchase #3	$100.62	13.836%	$114.5418	$114.54	$114.55	$114.50
Purchase #4	$233.69	12.363%	$262.5811	$262.58	$262.60	$262.60
Purchase #5	$67.82	7.373%	$72.8204	$72.82	$72.80	$72.80
Purchase #6	$37.97	10.676%	$42.0237	$42.02	$42.00	$42.00
Purchase #7	$53.58	9.648%	$58.7494	$58.75	$58.75	$58.70
7 purchase totals =	$788.85		$868.5779	$868.57	$868.55	$868.50