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	$7.43	3.801%	$7.7124	$7.71	$7.70	$7.70
Purchase #2	$187.36	12.225%	$210.2648	$210.26	$210.25	$210.30
Purchase #3	$112.99	13.682%	$128.4493	$128.45	$128.45	$128.40
Purchase #4	$183.81	3.573%	$190.3775	$190.38	$190.40	$190.40
Purchase #5	$153.73	13.601%	$174.6388	$174.64	$174.65	$174.60
Purchase #6	$184.60	6.446%	$196.4993	$196.50	$196.50	$196.50
Purchase #7	$117.53	9.186%	$128.3263	$128.33	$128.35	$128.30
7 purchase totals =	$947.45		$1,036.2684	$1,036.27	$1,036.30	$1,036.20