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	$231.94	10.111%	$255.3915	$255.39	$255.40	$255.40
Purchase #2	$28.71	9.721%	$31.5009	$31.50	$31.50	$31.50
Purchase #3	$72.49	8.649%	$78.7597	$78.76	$78.75	$78.80
Purchase #4	$89.30	10.403%	$98.5899	$98.59	$98.60	$98.60
Purchase #5	$17.86	10.590%	$19.7514	$19.75	$19.75	$19.80
Purchase #6	$239.61	3.729%	$248.5451	$248.55	$248.55	$248.50
Purchase #7	$72.40	10.496%	$79.9991	$80.00	$80.00	$80.00
7 purchase totals =	$752.31		$812.5376	$812.54	$812.55	$812.60