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	$120.55	7.655%	$129.7781	$129.78	$129.80	$129.80
Purchase #2	$122.74	4.546%	$128.3198	$128.32	$128.30	$128.30
Purchase #3	$102.88	13.632%	$116.9046	$116.90	$116.90	$116.90
Purchase #4	$171.67	9.317%	$187.6645	$187.66	$187.65	$187.70
Purchase #5	$57.58	3.391%	$59.5325	$59.53	$59.55	$59.50
Purchase #6	$111.30	10.846%	$123.3716	$123.37	$123.35	$123.40
Purchase #7	$183.72	7.249%	$197.0379	$197.04	$197.05	$197.00
7 purchase totals =	$870.44		$942.6090	$942.60	$942.60	$942.60