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	$95.30	5.456%	$100.4996	$100.50	$100.50	$100.50
Purchase #2	$21.32	3.658%	$22.0999	$22.10	$22.10	$22.10
Purchase #3	$187.58	4.752%	$196.4938	$196.49	$196.50	$196.50
Purchase #4	$31.78	3.388%	$32.8567	$32.86	$32.85	$32.90
Purchase #5	$84.62	5.831%	$89.5542	$89.55	$89.55	$89.60
Purchase #6	$166.84	4.491%	$174.3328	$174.33	$174.35	$174.30
Purchase #7	$228.74	12.317%	$256.9139	$256.91	$256.90	$256.90
7 purchase totals =	$816.18		$872.7509	$872.74	$872.75	$872.80